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 $91.85   11.255%   $102.1877   $102.19   $102.20   $102.20  
  Purchase #2 $78.53   8.371%   $85.1037   $85.10   $85.10   $85.10  
  Purchase #3 $56.53   10.353%   $62.3826   $62.38   $62.40   $62.40  
  Purchase #4 $109.42   3.768%   $113.5429   $113.54   $113.55   $113.50  
  Purchase #5 $168.84   9.541%   $184.949   $184.95   $184.95   $184.90  
  Purchase #6 $106.62   4.466%   $111.3816   $111.38   $111.40   $111.40  
  Purchase #7 $189.57   8.193%   $205.1015   $205.10   $205.10   $205.10  
  7 purchase totals = $801.36       $864.6490   $864.64   $864.70   $864.60