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 $222.55   9.172%   $242.9623   $242.96   $242.95   $243.00  
  Purchase #2 $195.57   11.814%   $218.6746   $218.67   $218.65   $218.70  
  Purchase #3 $39.26   4.123%   $40.8787   $40.88   $40.90   $40.90  
  Purchase #4 $139.27   11.828%   $155.7429   $155.74   $155.75   $155.70  
  Purchase #5 $148.65   9.216%   $162.3496   $162.35   $162.35   $162.30  
  Purchase #6 $35.68   6.457%   $37.9839   $37.98   $38.00   $38.00  
  Purchase #7 $60.97   6.157%   $64.7239   $64.72   $64.70   $64.70  
  7 purchase totals = $841.95       $923.3159   $923.30   $923.30   $923.30