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 $192.34   5.698%   $203.2995   $203.30   $203.30   $203.30  
  Purchase #2 $113.96   8.104%   $123.1953   $123.20   $123.20   $123.20  
  Purchase #3 $69.38   10.465%   $76.6406   $76.64   $76.65   $76.60  
  Purchase #4 $132.55   11.456%   $147.7349   $147.73   $147.75   $147.70  
  Purchase #5 $83.63   10.660%   $92.545   $92.55   $92.55   $92.50  
  Purchase #6 $88.30   6.837%   $94.3371   $94.34   $94.35   $94.30  
  Purchase #7 $9.70   9.661%   $10.6371   $10.64   $10.65   $10.60  
  7 purchase totals = $689.86       $748.3895   $748.40   $748.45   $748.20