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 $110.92   12.270%   $124.5299   $124.53   $124.55   $124.50  
  Purchase #2 $101.74   3.104%   $104.898   $104.90   $104.90   $104.90  
  Purchase #3 $96.38   13.214%   $109.1157   $109.12   $109.10   $109.10  
  Purchase #4 $139.28   5.471%   $146.9   $146.90   $146.90   $146.90  
  Purchase #5 $165.95   6.290%   $176.3883   $176.39   $176.40   $176.40  
  Purchase #6 $136.63   4.358%   $142.5843   $142.58   $142.60   $142.60  
  Purchase #7 $121.73   5.521%   $128.4507   $128.45   $128.45   $128.50  
  7 purchase totals = $872.63       $932.8669   $932.87   $932.90   $932.90