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 $12.65   12.291%   $14.2048   $14.20   $14.20   $14.20  
  Purchase #2 $192.55   8.620%   $209.1478   $209.15   $209.15   $209.10  
  Purchase #3 $117.75   5.532%   $124.2639   $124.26   $124.25   $124.30  
  Purchase #4 $60.27   7.176%   $64.595   $64.60   $64.60   $64.60  
  Purchase #5 $66.37   4.430%   $69.3102   $69.31   $69.30   $69.30  
  Purchase #6 $221.66   4.622%   $231.9051   $231.91   $231.90   $231.90  
  Purchase #7 $153.74   11.776%   $171.8444   $171.84   $171.85   $171.80  
  7 purchase totals = $824.99       $885.2712   $885.27   $885.25   $885.20