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 $62.31   11.355%   $69.3853   $69.39   $69.40   $69.40  
  Purchase #2 $195.72   8.864%   $213.0686   $213.07   $213.05   $213.10  
  Purchase #3 $197.60   4.803%   $207.0907   $207.09   $207.10   $207.10  
  Purchase #4 $215.48   12.317%   $242.0207   $242.02   $242.00   $242.00  
  Purchase #5 $116.97   8.572%   $126.9967   $127.00   $127.00   $127.00  
  Purchase #6 $46.83   8.321%   $50.7267   $50.73   $50.75   $50.70  
  Purchase #7 $68.68   8.450%   $74.4835   $74.48   $74.50   $74.50  
  7 purchase totals = $903.59       $983.7722   $983.78   $983.80   $983.80