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 $219.38   10.194%   $241.7436   $241.74   $241.75   $241.70  
  Purchase #2 $47.56   5.551%   $50.2001   $50.20   $50.20   $50.20  
  Purchase #3 $123.91   11.453%   $138.1014   $138.10   $138.10   $138.10  
  Purchase #4 $162.43   7.674%   $174.8949   $174.89   $174.90   $174.90  
  Purchase #5 $51.30   8.164%   $55.4881   $55.49   $55.50   $55.50  
  Purchase #6 $203.40   5.568%   $214.7253   $214.73   $214.75   $214.70  
  Purchase #7 $108.56   8.519%   $117.8082   $117.81   $117.80   $117.80  
  7 purchase totals = $916.54       $992.9616   $992.96   $993.00   $992.90