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 $64.26   3.822%   $66.716   $66.72   $66.70   $66.70  
  Purchase #2 $71.58   3.204%   $73.8734   $73.87   $73.85   $73.90  
  Purchase #3 $73.67   10.474%   $81.3862   $81.39   $81.40   $81.40  
  Purchase #4 $187.32   10.307%   $206.6271   $206.63   $206.65   $206.60  
  Purchase #5 $87.79   9.267%   $95.9255   $95.93   $95.95   $95.90  
  Purchase #6 $247.47   5.423%   $260.8903   $260.89   $260.90   $260.90  
  Purchase #7 $162.89   7.523%   $175.1442   $175.14   $175.15   $175.10  
  7 purchase totals = $894.98       $960.5627   $960.57   $960.60   $960.50