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 $219.95   12.578%   $247.6153   $247.62   $247.60   $247.60  
  Purchase #2 $59.53   12.694%   $67.0867   $67.09   $67.10   $67.10  
  Purchase #3 $116.58   4.790%   $122.1642   $122.16   $122.15   $122.20  
  Purchase #4 $183.77   6.178%   $195.1233   $195.12   $195.10   $195.10  
  Purchase #5 $87.98   6.386%   $93.5984   $93.60   $93.60   $93.60  
  Purchase #6 $40.56   11.709%   $45.3092   $45.31   $45.30   $45.30  
  Purchase #7 $163.36   10.686%   $180.8166   $180.82   $180.80   $180.80  
  7 purchase totals = $871.73       $951.7137   $951.72   $951.65   $951.70