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 $217.61   13.479%   $246.9417   $246.94   $246.95   $246.90  
  Purchase #2 $10.85   10.481%   $11.9872   $11.99   $12.00   $12.00  
  Purchase #3 $105.92   9.476%   $115.957   $115.96   $115.95   $116.00  
  Purchase #4 $128.44   9.584%   $140.7497   $140.75   $140.75   $140.70  
  Purchase #5 $238.80   11.780%   $266.9306   $266.93   $266.95   $266.90  
  Purchase #6 $194.39   8.177%   $210.2853   $210.29   $210.30   $210.30  
  Purchase #7 $245.68   10.420%   $271.2799   $271.28   $271.30   $271.30  
  7 purchase totals = $1,141.69       $1,264.1314   $1,264.14   $1,264.20   $1,264.10