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 $86.71   10.452%   $95.7729   $95.77   $95.75   $95.80  
  Purchase #2 $107.25   13.389%   $121.6097   $121.61   $121.60   $121.60  
  Purchase #3 $94.34   8.667%   $102.5164   $102.52   $102.50   $102.50  
  Purchase #4 $191.41   8.486%   $207.6531   $207.65   $207.65   $207.70  
  Purchase #5 $45.67   8.152%   $49.393   $49.39   $49.40   $49.40  
  Purchase #6 $131.40   3.853%   $136.4628   $136.46   $136.45   $136.50  
  Purchase #7 $224.43   6.562%   $239.1571   $239.16   $239.15   $239.20  
  7 purchase totals = $881.21       $952.5650   $952.56   $952.50   $952.70