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 $191.32   3.491%   $197.999   $198.00   $198.00   $198.00  
  Purchase #2 $246.76   13.472%   $280.0035   $280.00   $280.00   $280.00  
  Purchase #3 $168.53   3.245%   $173.9988   $174.00   $174.00   $174.00  
  Purchase #4 $250.69   9.597%   $274.7487   $274.75   $274.75   $274.70  
  Purchase #5 $95.53   11.706%   $106.7127   $106.71   $106.70   $106.70  
  Purchase #6 $178.89   8.635%   $194.3372   $194.34   $194.35   $194.30  
  Purchase #7 $64.76   13.552%   $73.5363   $73.54   $73.55   $73.50  
  7 purchase totals = $1,196.48       $1,301.3362   $1,301.34   $1,301.35   $1,301.20