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 $225.82   8.798%   $245.6876   $245.69   $245.70   $245.70  
  Purchase #2 $206.39   6.804%   $220.4328   $220.43   $220.45   $220.40  
  Purchase #3 $121.46   3.239%   $125.3941   $125.39   $125.40   $125.40  
  Purchase #4 $237.94   9.133%   $259.6711   $259.67   $259.65   $259.70  
  Purchase #5 $85.67   6.347%   $91.1075   $91.11   $91.10   $91.10  
  Purchase #6 $199.82   11.702%   $223.2029   $223.20   $223.20   $223.20  
  Purchase #7 $99.43   6.532%   $105.9248   $105.92   $105.90   $105.90  
  7 purchase totals = $1,176.53       $1,271.4208   $1,271.41   $1,271.40   $1,271.40