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 $236.83   3.528%   $245.1854   $245.19   $245.20   $245.20  
  Purchase #2 $176.82   10.694%   $195.7291   $195.73   $195.75   $195.70  
  Purchase #3 $187.93   8.853%   $204.5674   $204.57   $204.55   $204.60  
  Purchase #4 $94.45   8.282%   $102.2723   $102.27   $102.25   $102.30  
  Purchase #5 $87.80   5.451%   $92.586   $92.59   $92.60   $92.60  
  Purchase #6 $203.89   11.773%   $227.894   $227.89   $227.90   $227.90  
  Purchase #7 $167.84   4.164%   $174.8289   $174.83   $174.85   $174.80  
  7 purchase totals = $1,155.56       $1,243.0631   $1,243.07   $1,243.10   $1,243.10