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 $81.39   12.415%   $91.4946   $91.49   $91.50   $91.50  
  Purchase #2 $225.55   12.565%   $253.8904   $253.89   $253.90   $253.90  
  Purchase #3 $96.97   6.151%   $102.9346   $102.93   $102.95   $102.90  
  Purchase #4 $200.78   13.103%   $227.0882   $227.09   $227.10   $227.10  
  Purchase #5 $36.26   6.141%   $38.4867   $38.49   $38.50   $38.50  
  Purchase #6 $65.80   11.824%   $73.5802   $73.58   $73.60   $73.60  
  Purchase #7 $87.30   10.517%   $96.4813   $96.48   $96.50   $96.50  
  7 purchase totals = $794.05       $883.9560   $883.95   $884.05   $884.00