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 $186.71   11.714%   $208.5812   $208.58   $208.60   $208.60  
  Purchase #2 $56.80   10.307%   $62.6544   $62.65   $62.65   $62.70  
  Purchase #3 $48.90   6.248%   $51.9553   $51.96   $51.95   $52.00  
  Purchase #4 $238.27   7.848%   $256.9694   $256.97   $256.95   $257.00  
  Purchase #5 $127.60   3.157%   $131.6283   $131.63   $131.65   $131.60  
  Purchase #6 $127.39   3.814%   $132.2487   $132.25   $132.25   $132.20  
  Purchase #7 $29.81   13.533%   $33.8442   $33.84   $33.85   $33.80  
  7 purchase totals = $815.48       $877.8815   $877.88   $877.90   $877.90