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 $55.56   9.427%   $60.7976   $60.80   $60.80   $60.80  
  Purchase #2 $64.53   3.809%   $66.9879   $66.99   $67.00   $67.00  
  Purchase #3 $40.54   5.758%   $42.8743   $42.87   $42.85   $42.90  
  Purchase #4 $132.41   10.483%   $146.2905   $146.29   $146.30   $146.30  
  Purchase #5 $220.77   11.796%   $246.812   $246.81   $246.80   $246.80  
  Purchase #6 $161.43   7.555%   $173.626   $173.63   $173.65   $173.60  
  Purchase #7 $201.90   4.508%   $211.0017   $211.00   $211.00   $211.00  
  7 purchase totals = $877.14       $948.3900   $948.39   $948.40   $948.40