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 $162.95   6.199%   $173.0513   $173.05   $173.05   $173.10  
  Purchase #2 $21.28   6.863%   $22.7404   $22.74   $22.75   $22.70  
  Purchase #3 $153.31   6.463%   $163.2184   $163.22   $163.20   $163.20  
  Purchase #4 $57.84   8.235%   $62.6031   $62.60   $62.60   $62.60  
  Purchase #5 $107.40   11.505%   $119.7564   $119.76   $119.75   $119.80  
  Purchase #6 $195.45   4.388%   $204.0263   $204.03   $204.05   $204.00  
  Purchase #7 $135.71   3.338%   $140.24   $140.24   $140.25   $140.20  
  7 purchase totals = $833.94       $885.6359   $885.64   $885.65   $885.60