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 $209.41   11.246%   $232.9602   $232.96   $232.95   $233.00  
  Purchase #2 $162.82   8.472%   $176.6141   $176.61   $176.60   $176.60  
  Purchase #3 $69.50   11.814%   $77.7107   $77.71   $77.70   $77.70  
  Purchase #4 $16.90   9.458%   $18.4984   $18.50   $18.50   $18.50  
  Purchase #5 $9.26   9.135%   $10.1059   $10.11   $10.10   $10.10  
  Purchase #6 $213.87   3.563%   $221.4902   $221.49   $221.50   $221.50  
  Purchase #7 $23.40   5.306%   $24.6416   $24.64   $24.65   $24.60  
  7 purchase totals = $705.16       $762.0211   $762.02   $762.00   $762.00