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 $174.61   13.228%   $197.7074   $197.71   $197.70   $197.70  
  Purchase #2 $140.82   5.631%   $148.7496   $148.75   $148.75   $148.70  
  Purchase #3 $101.73   13.255%   $115.2143   $115.21   $115.20   $115.20  
  Purchase #4 $239.38   6.267%   $254.3819   $254.38   $254.40   $254.40  
  Purchase #5 $207.30   5.362%   $218.4154   $218.42   $218.40   $218.40  
  Purchase #6 $62.25   8.374%   $67.4628   $67.46   $67.45   $67.50  
  Purchase #7 $106.31   11.703%   $118.7515   $118.75   $118.75   $118.80  
  7 purchase totals = $1,032.40       $1,120.6829   $1,120.68   $1,120.65   $1,120.70