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 $242.90   4.691%   $254.2944   $254.29   $254.30   $254.30  
  Purchase #2 $112.95   11.135%   $125.527   $125.53   $125.55   $125.50  
  Purchase #3 $177.63   6.587%   $189.3305   $189.33   $189.35   $189.30  
  Purchase #4 $238.63   11.307%   $265.6119   $265.61   $265.60   $265.60  
  Purchase #5 $150.36   6.311%   $159.8492   $159.85   $159.85   $159.80  
  Purchase #6 $87.28   8.290%   $94.5155   $94.52   $94.50   $94.50  
  Purchase #7 $148.78   9.555%   $162.9959   $163.00   $163.00   $163.00  
  7 purchase totals = $1,158.53       $1,252.1244   $1,252.13   $1,252.15   $1,252.00