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 $217.65   3.464%   $225.1894   $225.19   $225.20   $225.20  
  Purchase #2 $110.90   6.109%   $117.6749   $117.67   $117.65   $117.70  
  Purchase #3 $87.73   9.315%   $95.902   $95.90   $95.90   $95.90  
  Purchase #4 $73.66   4.690%   $77.1147   $77.11   $77.10   $77.10  
  Purchase #5 $175.66   7.222%   $188.3462   $188.35   $188.35   $188.30  
  Purchase #6 $170.30   8.744%   $185.191   $185.19   $185.20   $185.20  
  Purchase #7 $114.71   6.520%   $122.1891   $122.19   $122.20   $122.20  
  7 purchase totals = $950.61       $1,011.6073   $1,011.60   $1,011.60   $1,011.60