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 $55.43   6.362%   $58.9565   $58.96   $58.95   $59.00  
  Purchase #2 $221.68   10.827%   $245.6813   $245.68   $245.70   $245.70  
  Purchase #3 $10.39   13.245%   $11.7662   $11.77   $11.75   $11.80  
  Purchase #4 $162.48   5.509%   $171.431   $171.43   $171.45   $171.40  
  Purchase #5 $125.34   13.380%   $142.1105   $142.11   $142.10   $142.10  
  Purchase #6 $217.49   13.773%   $247.4449   $247.44   $247.45   $247.40  
  Purchase #7 $40.56   8.389%   $43.9626   $43.96   $43.95   $44.00  
  7 purchase totals = $833.37       $921.3530   $921.35   $921.35   $921.40