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 $235.77   11.146%   $262.0489   $262.05   $262.05   $262.00  
  Purchase #2 $183.93   12.410%   $206.7557   $206.76   $206.75   $206.80  
  Purchase #3 $226.69   9.185%   $247.5115   $247.51   $247.50   $247.50  
  Purchase #4 $166.86   7.204%   $178.8806   $178.88   $178.90   $178.90  
  Purchase #5 $70.79   6.783%   $75.5917   $75.59   $75.60   $75.60  
  Purchase #6 $62.38   4.486%   $65.1784   $65.18   $65.20   $65.20  
  Purchase #7 $199.76   5.704%   $211.1543   $211.15   $211.15   $211.20  
  7 purchase totals = $1,146.18       $1,247.1211   $1,247.12   $1,247.15   $1,247.20