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 $58.72   12.214%   $65.8921   $65.89   $65.90   $65.90  
  Purchase #2 $235.96   7.756%   $254.2611   $254.26   $254.25   $254.30  
  Purchase #3 $195.65   4.105%   $203.6814   $203.68   $203.70   $203.70  
  Purchase #4 $58.37   11.207%   $64.9115   $64.91   $64.90   $64.90  
  Purchase #5 $135.94   6.782%   $145.1595   $145.16   $145.15   $145.20  
  Purchase #6 $165.64   4.300%   $172.7625   $172.76   $172.75   $172.80  
  Purchase #7 $15.55   11.110%   $17.2776   $17.28   $17.30   $17.30  
  7 purchase totals = $865.83       $923.9457   $923.94   $923.95   $924.10