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 $111.71   11.585%   $124.6516   $124.65   $124.65   $124.70  
  Purchase #2 $119.97   5.718%   $126.8299   $126.83   $126.85   $126.80  
  Purchase #3 $112.89   12.596%   $127.1096   $127.11   $127.10   $127.10  
  Purchase #4 $235.61   12.663%   $265.4453   $265.45   $265.45   $265.40  
  Purchase #5 $120.75   7.625%   $129.9572   $129.96   $129.95   $130.00  
  Purchase #6 $60.78   8.603%   $66.0089   $66.01   $66.00   $66.00  
  Purchase #7 $32.94   7.155%   $35.2969   $35.30   $35.30   $35.30  
  7 purchase totals = $794.65       $875.2994   $875.31   $875.30   $875.30