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 $53.51   8.321%   $57.9626   $57.96   $57.95   $58.00  
  Purchase #2 $168.83   8.164%   $182.6133   $182.61   $182.60   $182.60  
  Purchase #3 $59.39   5.695%   $62.7723   $62.77   $62.75   $62.80  
  Purchase #4 $77.92   8.790%   $84.7692   $84.77   $84.75   $84.80  
  Purchase #5 $149.52   5.149%   $157.2188   $157.22   $157.20   $157.20  
  Purchase #6 $205.49   5.628%   $217.055   $217.06   $217.05   $217.10  
  Purchase #7 $91.48   6.654%   $97.5671   $97.57   $97.55   $97.60  
  7 purchase totals = $806.14       $859.9583   $859.96   $859.85   $860.10