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 $196.58   10.821%   $217.8519   $217.85   $217.85   $217.90  
  Purchase #2 $59.28   12.382%   $66.62   $66.62   $66.60   $66.60  
  Purchase #3 $160.32   7.374%   $172.142   $172.14   $172.15   $172.10  
  Purchase #4 $213.94   6.394%   $227.6193   $227.62   $227.60   $227.60  
  Purchase #5 $70.43   13.370%   $79.8465   $79.85   $79.85   $79.80  
  Purchase #6 $21.69   12.348%   $24.3683   $24.37   $24.35   $24.40  
  Purchase #7 $162.50   8.541%   $176.3791   $176.38   $176.40   $176.40  
  7 purchase totals = $884.74       $964.8271   $964.83   $964.80   $964.80