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 $66.73   12.369%   $74.9838   $74.98   $75.00   $75.00  
  Purchase #2 $120.91   5.741%   $127.8514   $127.85   $127.85   $127.90  
  Purchase #3 $187.61   6.282%   $199.3957   $199.40   $199.40   $199.40  
  Purchase #4 $128.28   7.531%   $137.9408   $137.94   $137.95   $137.90  
  Purchase #5 $215.66   8.475%   $233.9372   $233.94   $233.95   $233.90  
  Purchase #6 $234.63   11.662%   $261.9926   $261.99   $262.00   $262.00  
  Purchase #7 $122.36   7.578%   $131.6324   $131.63   $131.65   $131.60  
  7 purchase totals = $1,076.18       $1,167.7339   $1,167.73   $1,167.80   $1,167.70