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 $34.70   4.302%   $36.1928   $36.19   $36.20   $36.20  
  Purchase #2 $82.28   12.593%   $92.6415   $92.64   $92.65   $92.60  
  Purchase #3 $205.54   3.837%   $213.4266   $213.43   $213.45   $213.40  
  Purchase #4 $250.62   7.296%   $268.9052   $268.91   $268.90   $268.90  
  Purchase #5 $156.28   12.121%   $175.2227   $175.22   $175.20   $175.20  
  Purchase #6 $98.36   11.464%   $109.636   $109.64   $109.65   $109.60  
  Purchase #7 $21.40   7.520%   $23.0093   $23.01   $23.00   $23.00  
  7 purchase totals = $849.18       $919.0341   $919.04   $919.05   $918.90