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 $247.83   11.595%   $276.5659   $276.57   $276.55   $276.60  
  Purchase #2 $100.68   4.728%   $105.4402   $105.44   $105.45   $105.40  
  Purchase #3 $130.35   5.839%   $137.9611   $137.96   $137.95   $138.00  
  Purchase #4 $113.76   10.406%   $125.5979   $125.60   $125.60   $125.60  
  Purchase #5 $67.33   3.864%   $69.9316   $69.93   $69.95   $69.90  
  Purchase #6 $165.42   9.103%   $180.4782   $180.48   $180.50   $180.50  
  Purchase #7 $122.84   4.664%   $128.5693   $128.57   $128.55   $128.60  
  7 purchase totals = $948.21       $1,024.5442   $1,024.55   $1,024.55   $1,024.60