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 $68.90   4.344%   $71.893   $71.89   $71.90   $71.90  
  Purchase #2 $40.90   12.347%   $45.9499   $45.95   $45.95   $45.90  
  Purchase #3 $229.57   3.147%   $236.7946   $236.79   $236.80   $236.80  
  Purchase #4 $245.34   7.662%   $264.138   $264.14   $264.15   $264.10  
  Purchase #5 $61.92   12.634%   $69.743   $69.74   $69.75   $69.70  
  Purchase #6 $200.29   5.312%   $210.9294   $210.93   $210.95   $210.90  
  Purchase #7 $124.27   11.865%   $139.0146   $139.01   $139.00   $139.00  
  7 purchase totals = $971.19       $1,038.4625   $1,038.45   $1,038.50   $1,038.30