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 $59.84   3.691%   $62.0487   $62.05   $62.05   $62.00  
  Purchase #2 $119.42   13.591%   $135.6504   $135.65   $135.65   $135.70  
  Purchase #3 $101.35   3.298%   $104.6925   $104.69   $104.70   $104.70  
  Purchase #4 $157.78   5.477%   $166.4216   $166.42   $166.40   $166.40  
  Purchase #5 $13.35   6.131%   $14.1685   $14.17   $14.15   $14.20  
  Purchase #6 $221.70   10.323%   $244.5861   $244.59   $244.60   $244.60  
  Purchase #7 $131.51   8.341%   $142.4792   $142.48   $142.50   $142.50  
  7 purchase totals = $804.95       $870.0470   $870.05   $870.05   $870.10