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 $84.74   10.860%   $93.9428   $93.94   $93.95   $93.90  
  Purchase #2 $138.63   7.799%   $149.4418   $149.44   $149.45   $149.40  
  Purchase #3 $5.73   6.765%   $6.1176   $6.12   $6.10   $6.10  
  Purchase #4 $44.39   13.522%   $50.3924   $50.39   $50.40   $50.40  
  Purchase #5 $246.78   7.211%   $264.5753   $264.58   $264.60   $264.60  
  Purchase #6 $119.52   11.579%   $133.3592   $133.36   $133.35   $133.40  
  Purchase #7 $33.33   4.262%   $34.7505   $34.75   $34.75   $34.80  
  7 purchase totals = $673.12       $732.5796   $732.58   $732.60   $732.60