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 $125.69   12.735%   $141.6966   $141.70   $141.70   $141.70  
  Purchase #2 $203.97   8.527%   $221.3625   $221.36   $221.35   $221.40  
  Purchase #3 $72.68   6.335%   $77.2843   $77.28   $77.30   $77.30  
  Purchase #4 $216.41   11.734%   $241.8035   $241.80   $241.80   $241.80  
  Purchase #5 $89.37   13.826%   $101.7263   $101.73   $101.75   $101.70  
  Purchase #6 $17.76   9.143%   $19.3838   $19.38   $19.40   $19.40  
  Purchase #7 $165.64   9.401%   $181.2118   $181.21   $181.20   $181.20  
  7 purchase totals = $891.52       $984.4688   $984.46   $984.50   $984.50