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 $219.48   12.519%   $246.9567   $246.96   $246.95   $247.00  
  Purchase #2 $96.88   5.508%   $102.2162   $102.22   $102.20   $102.20  
  Purchase #3 $162.35   11.582%   $181.1534   $181.15   $181.15   $181.20  
  Purchase #4 $100.61   12.573%   $113.2597   $113.26   $113.25   $113.30  
  Purchase #5 $54.67   9.300%   $59.7543   $59.75   $59.75   $59.80  
  Purchase #6 $231.77   7.775%   $249.7901   $249.79   $249.80   $249.80  
  Purchase #7 $114.80   13.566%   $130.3738   $130.37   $130.35   $130.40  
  7 purchase totals = $980.56       $1,083.5042   $1,083.50   $1,083.45   $1,083.70