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 $87.73   6.834%   $93.7255   $93.73   $93.75   $93.70  
  Purchase #2 $96.88   5.702%   $102.4041   $102.40   $102.40   $102.40  
  Purchase #3 $178.61   11.633%   $199.3877   $199.39   $199.40   $199.40  
  Purchase #4 $154.26   8.175%   $166.8708   $166.87   $166.85   $166.90  
  Purchase #5 $154.47   12.405%   $173.632   $173.63   $173.65   $173.60  
  Purchase #6 $182.67   7.572%   $196.5018   $196.50   $196.50   $196.50  
  Purchase #7 $230.98   13.802%   $262.8599   $262.86   $262.85   $262.90  
  7 purchase totals = $1,085.60       $1,195.3818   $1,195.38   $1,195.40   $1,195.40