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 $82.61   12.759%   $93.1502   $93.15   $93.15   $93.20  
  Purchase #2 $210.27   11.438%   $234.3207   $234.32   $234.30   $234.30  
  Purchase #3 $87.27   6.255%   $92.7287   $92.73   $92.75   $92.70  
  Purchase #4 $156.96   13.438%   $178.0523   $178.05   $178.05   $178.10  
  Purchase #5 $160.41   6.302%   $170.519   $170.52   $170.50   $170.50  
  Purchase #6 $164.46   4.383%   $171.6683   $171.67   $171.65   $171.70  
  Purchase #7 $22.69   13.637%   $25.7842   $25.78   $25.80   $25.80  
  7 purchase totals = $884.67       $966.2234   $966.22   $966.20   $966.30