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 $148.79   6.349%   $158.2367   $158.24   $158.25   $158.20  
  Purchase #2 $55.68   8.825%   $60.5938   $60.59   $60.60   $60.60  
  Purchase #3 $179.77   6.213%   $190.9391   $190.94   $190.95   $190.90  
  Purchase #4 $195.90   3.488%   $202.733   $202.73   $202.75   $202.70  
  Purchase #5 $144.46   5.629%   $152.5917   $152.59   $152.60   $152.60  
  Purchase #6 $138.89   11.506%   $154.8707   $154.87   $154.85   $154.90  
  Purchase #7 $250.62   10.178%   $276.1281   $276.13   $276.15   $276.10  
  7 purchase totals = $1,114.11       $1,196.0931   $1,196.09   $1,196.15   $1,196.00