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 $58.54   13.207%   $66.2714   $66.27   $66.25   $66.30  
  Purchase #2 $243.88   7.795%   $262.8904   $262.89   $262.90   $262.90  
  Purchase #3 $152.43   12.733%   $171.8389   $171.84   $171.85   $171.80  
  Purchase #4 $140.49   11.636%   $156.8374   $156.84   $156.85   $156.80  
  Purchase #5 $40.26   3.416%   $41.6353   $41.64   $41.65   $41.60  
  Purchase #6 $98.62   8.451%   $106.9544   $106.95   $106.95   $107.00  
  Purchase #7 $200.57   13.458%   $227.5627   $227.56   $227.55   $227.60  
  7 purchase totals = $934.79       $1,033.9905   $1,033.99   $1,034.00   $1,034.00