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 $184.55   13.410%   $209.2982   $209.30   $209.30   $209.30  
  Purchase #2 $133.37   9.440%   $145.9601   $145.96   $145.95   $146.00  
  Purchase #3 $69.55   13.153%   $78.6979   $78.70   $78.70   $78.70  
  Purchase #4 $191.27   3.341%   $197.6603   $197.66   $197.65   $197.70  
  Purchase #5 $148.47   12.463%   $166.9738   $166.97   $166.95   $167.00  
  Purchase #6 $131.60   7.221%   $141.1028   $141.10   $141.10   $141.10  
  Purchase #7 $86.63   8.827%   $94.2768   $94.28   $94.30   $94.30  
  7 purchase totals = $945.44       $1,033.9699   $1,033.97   $1,033.95   $1,034.10