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 $70.62   3.470%   $73.0705   $73.07   $73.05   $73.10  
  Purchase #2 $79.68   4.619%   $83.3604   $83.36   $83.35   $83.40  
  Purchase #3 $176.41   3.271%   $182.1804   $182.18   $182.20   $182.20  
  Purchase #4 $95.36   8.131%   $103.1137   $103.11   $103.10   $103.10  
  Purchase #5 $238.86   5.667%   $252.3962   $252.40   $252.40   $252.40  
  Purchase #6 $182.50   9.229%   $199.3429   $199.34   $199.35   $199.30  
  Purchase #7 $22.33   12.850%   $25.1994   $25.20   $25.20   $25.20  
  7 purchase totals = $865.76       $918.6635   $918.66   $918.65   $918.70