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 $172.44   13.270%   $195.3228   $195.32   $195.30   $195.30  
  Purchase #2 $208.57   4.277%   $217.4905   $217.49   $217.50   $217.50  
  Purchase #3 $123.85   10.533%   $136.8951   $136.90   $136.90   $136.90  
  Purchase #4 $110.73   9.497%   $121.246   $121.25   $121.25   $121.20  
  Purchase #5 $232.73   10.542%   $257.2644   $257.26   $257.25   $257.30  
  Purchase #6 $131.60   6.739%   $140.4685   $140.47   $140.45   $140.50  
  Purchase #7 $151.46   9.499%   $165.8472   $165.85   $165.85   $165.80  
  7 purchase totals = $1,131.38       $1,234.5345   $1,234.54   $1,234.50   $1,234.50