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 $241.94   13.636%   $274.9309   $274.93   $274.95   $274.90  
  Purchase #2 $239.61   13.179%   $271.1882   $271.19   $271.20   $271.20  
  Purchase #3 $190.87   6.742%   $203.7385   $203.74   $203.75   $203.70  
  Purchase #4 $73.44   4.460%   $76.7154   $76.72   $76.70   $76.70  
  Purchase #5 $195.25   8.288%   $211.4323   $211.43   $211.45   $211.40  
  Purchase #6 $150.95   7.856%   $162.8086   $162.81   $162.80   $162.80  
  Purchase #7 $117.34   7.526%   $126.171   $126.17   $126.15   $126.20  
  7 purchase totals = $1,209.40       $1,326.9849   $1,326.99   $1,327.00   $1,326.90