Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $177.63   12.228%   $199.3506   $199.35   $199.35   $199.40  
  Purchase #2 $227.44   8.399%   $246.5427   $246.54   $246.55   $246.50  
  Purchase #3 $145.32   4.195%   $151.4162   $151.42   $151.40   $151.40  
  Purchase #4 $105.67   6.446%   $112.4815   $112.48   $112.50   $112.50  
  Purchase #5 $108.29   5.861%   $114.6369   $114.64   $114.65   $114.60  
  Purchase #6 $198.68   13.644%   $225.7879   $225.79   $225.80   $225.80  
  Purchase #7 $241.68   13.771%   $274.9618   $274.96   $274.95   $275.00  
  7 purchase totals = $1,204.71       $1,325.1776   $1,325.18   $1,325.20   $1,325.20