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 $56.38   5.585%   $59.5288   $59.53   $59.55   $59.50  
  Purchase #2 $169.90   11.816%   $189.9754   $189.98   $190.00   $190.00  
  Purchase #3 $186.27   12.602%   $209.7437   $209.74   $209.75   $209.70  
  Purchase #4 $225.69   5.262%   $237.5658   $237.57   $237.55   $237.60  
  Purchase #5 $124.68   8.348%   $135.0883   $135.09   $135.10   $135.10  
  Purchase #6 $45.69   5.803%   $48.3414   $48.34   $48.35   $48.30  
  Purchase #7 $200.69   11.682%   $224.1346   $224.13   $224.15   $224.10  
  7 purchase totals = $1,009.30       $1,104.3780   $1,104.38   $1,104.45   $1,104.30