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 $185.68   6.135%   $197.0715   $197.07   $197.05   $197.10  
  Purchase #2 $232.40   8.539%   $252.2446   $252.24   $252.25   $252.20  
  Purchase #3 $76.32   10.441%   $84.2886   $84.29   $84.30   $84.30  
  Purchase #4 $62.81   9.617%   $68.8504   $68.85   $68.85   $68.90  
  Purchase #5 $135.79   9.515%   $148.7104   $148.71   $148.70   $148.70  
  Purchase #6 $41.67   6.787%   $44.4981   $44.50   $44.50   $44.50  
  Purchase #7 $119.72   9.447%   $131.0299   $131.03   $131.05   $131.00  
  7 purchase totals = $854.39       $926.6935   $926.69   $926.70   $926.70