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 $109.41   13.244%   $123.9003   $123.90   $123.90   $123.90  
  Purchase #2 $127.30   4.791%   $133.3989   $133.40   $133.40   $133.40  
  Purchase #3 $105.92   10.431%   $116.9685   $116.97   $116.95   $117.00  
  Purchase #4 $246.31   12.323%   $276.6628   $276.66   $276.65   $276.70  
  Purchase #5 $105.33   13.176%   $119.2083   $119.21   $119.20   $119.20  
  Purchase #6 $167.85   3.684%   $174.0336   $174.03   $174.05   $174.00  
  Purchase #7 $65.31   5.609%   $68.9732   $68.97   $68.95   $69.00  
  7 purchase totals = $927.43       $1,013.1456   $1,013.14   $1,013.10   $1,013.20