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 $54.96   12.533%   $61.8481   $61.85   $61.85   $61.80  
  Purchase #2 $236.68   9.517%   $259.2048   $259.20   $259.20   $259.20  
  Purchase #3 $102.71   9.486%   $112.4531   $112.45   $112.45   $112.50  
  Purchase #4 $239.60   4.440%   $250.2382   $250.24   $250.25   $250.20  
  Purchase #5 $234.37   8.761%   $254.9032   $254.90   $254.90   $254.90  
  Purchase #6 $218.54   12.495%   $245.8466   $245.85   $245.85   $245.80  
  Purchase #7 $159.85   8.398%   $173.2742   $173.27   $173.25   $173.30  
  7 purchase totals = $1,246.71       $1,357.7682   $1,357.76   $1,357.75   $1,357.70