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 $174.92   11.764%   $195.4976   $195.50   $195.50   $195.50  
  Purchase #2 $227.56   5.160%   $239.3021   $239.30   $239.30   $239.30  
  Purchase #3 $194.40   13.660%   $220.955   $220.96   $220.95   $221.00  
  Purchase #4 $62.71   7.633%   $67.4967   $67.50   $67.50   $67.50  
  Purchase #5 $16.82   5.423%   $17.7321   $17.73   $17.75   $17.70  
  Purchase #6 $237.25   10.722%   $262.6879   $262.69   $262.70   $262.70  
  Purchase #7 $134.59   6.205%   $142.9413   $142.94   $142.95   $142.90  
  7 purchase totals = $1,048.25       $1,146.6127   $1,146.62   $1,146.65   $1,146.60