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 $59.46   3.872%   $61.7623   $61.76   $61.75   $61.80  
  Purchase #2 $242.64   9.392%   $265.4287   $265.43   $265.45   $265.40  
  Purchase #3 $74.76   13.592%   $84.9214   $84.92   $84.90   $84.90  
  Purchase #4 $73.77   4.773%   $77.291   $77.29   $77.30   $77.30  
  Purchase #5 $208.83   4.205%   $217.6113   $217.61   $217.60   $217.60  
  Purchase #6 $140.46   6.139%   $149.0828   $149.08   $149.10   $149.10  
  Purchase #7 $70.96   10.801%   $78.6244   $78.62   $78.60   $78.60  
  7 purchase totals = $870.88       $934.7219   $934.71   $934.70   $934.70