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 $241.62   5.649%   $255.2691   $255.27   $255.25   $255.30  
  Purchase #2 $122.92   6.455%   $130.8545   $130.85   $130.85   $130.90  
  Purchase #3 $237.74   8.414%   $257.7434   $257.74   $257.75   $257.70  
  Purchase #4 $58.66   8.256%   $63.503   $63.50   $63.50   $63.50  
  Purchase #5 $247.62   4.814%   $259.5404   $259.54   $259.55   $259.50  
  Purchase #6 $102.49   4.810%   $107.4198   $107.42   $107.40   $107.40  
  Purchase #7 $48.31   8.248%   $52.2946   $52.29   $52.30   $52.30  
  7 purchase totals = $1,059.36       $1,126.6248   $1,126.61   $1,126.60   $1,126.60