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 $243.75   4.220%   $254.0363   $254.04   $254.05   $254.00  
  Purchase #2 $135.93   12.525%   $152.9552   $152.96   $152.95   $153.00  
  Purchase #3 $198.58   9.481%   $217.4074   $217.41   $217.40   $217.40  
  Purchase #4 $230.66   8.184%   $249.5372   $249.54   $249.55   $249.50  
  Purchase #5 $51.27   12.487%   $57.6721   $57.67   $57.65   $57.70  
  Purchase #6 $102.89   5.579%   $108.6302   $108.63   $108.65   $108.60  
  Purchase #7 $114.79   13.667%   $130.4783   $130.48   $130.50   $130.50  
  7 purchase totals = $1,077.87       $1,170.7167   $1,170.73   $1,170.75   $1,170.70