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 $61.87   9.201%   $67.5627   $67.56   $67.55   $67.60  
  Purchase #2 $247.88   6.321%   $263.5485   $263.55   $263.55   $263.50  
  Purchase #3 $245.62   9.586%   $269.1651   $269.17   $269.15   $269.20  
  Purchase #4 $145.77   4.859%   $152.853   $152.85   $152.85   $152.90  
  Purchase #5 $164.38   5.706%   $173.7595   $173.76   $173.75   $173.80  
  Purchase #6 $90.71   4.346%   $94.6523   $94.65   $94.65   $94.70  
  Purchase #7 $88.49   5.310%   $93.1888   $93.19   $93.20   $93.20  
  7 purchase totals = $1,044.72       $1,114.7299   $1,114.73   $1,114.70   $1,114.90