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 $114.50   13.195%   $129.6083   $129.61   $129.60   $129.60  
  Purchase #2 $213.73   11.782%   $238.9117   $238.91   $238.90   $238.90  
  Purchase #3 $60.69   11.505%   $67.6724   $67.67   $67.65   $67.70  
  Purchase #4 $125.90   10.582%   $139.2227   $139.22   $139.20   $139.20  
  Purchase #5 $232.76   5.152%   $244.7518   $244.75   $244.75   $244.80  
  Purchase #6 $24.43   10.515%   $26.9988   $27.00   $27.00   $27.00  
  Purchase #7 $144.70   3.171%   $149.2884   $149.29   $149.30   $149.30  
  7 purchase totals = $916.71       $996.4541   $996.45   $996.40   $996.50