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 $197.84   10.699%   $219.0069   $219.01   $219.00   $219.00  
  Purchase #2 $95.90   13.868%   $109.1994   $109.20   $109.20   $109.20  
  Purchase #3 $25.94   6.178%   $27.5426   $27.54   $27.55   $27.50  
  Purchase #4 $121.86   11.173%   $135.4754   $135.48   $135.50   $135.50  
  Purchase #5 $58.80   9.157%   $64.1843   $64.18   $64.20   $64.20  
  Purchase #6 $242.91   7.847%   $261.9711   $261.97   $261.95   $262.00  
  Purchase #7 $244.29   8.838%   $265.8804   $265.88   $265.90   $265.90  
  7 purchase totals = $987.54       $1,083.2601   $1,083.26   $1,083.30   $1,083.30