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 $195.29   13.303%   $221.2694   $221.27   $221.25   $221.30  
  Purchase #2 $46.47   8.192%   $50.2768   $50.28   $50.30   $50.30  
  Purchase #3 $240.30   3.239%   $248.0833   $248.08   $248.10   $248.10  
  Purchase #4 $59.73   6.615%   $63.6811   $63.68   $63.70   $63.70  
  Purchase #5 $67.88   13.540%   $77.071   $77.07   $77.05   $77.10  
  Purchase #6 $154.50   11.533%   $172.3185   $172.32   $172.30   $172.30  
  Purchase #7 $181.96   4.186%   $189.5768   $189.58   $189.60   $189.60  
  7 purchase totals = $946.13       $1,022.2769   $1,022.28   $1,022.30   $1,022.40