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 $71.42   4.413%   $74.5718   $74.57   $74.55   $74.60  
  Purchase #2 $149.62   11.468%   $166.7784   $166.78   $166.80   $166.80  
  Purchase #3 $89.92   3.233%   $92.8271   $92.83   $92.85   $92.80  
  Purchase #4 $37.74   9.625%   $41.3725   $41.37   $41.35   $41.40  
  Purchase #5 $32.89   11.438%   $36.652   $36.65   $36.65   $36.70  
  Purchase #6 $248.92   10.613%   $275.3379   $275.34   $275.35   $275.30  
  Purchase #7 $170.75   3.788%   $177.218   $177.22   $177.20   $177.20  
  7 purchase totals = $801.26       $864.7577   $864.76   $864.75   $864.80