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 $193.96   6.212%   $206.0088   $206.01   $206.00   $206.00  
  Purchase #2 $37.53   10.193%   $41.3554   $41.36   $41.35   $41.40  
  Purchase #3 $17.45   13.296%   $19.7702   $19.77   $19.75   $19.80  
  Purchase #4 $205.28   4.168%   $213.8361   $213.84   $213.85   $213.80  
  Purchase #5 $175.88   12.732%   $198.273   $198.27   $198.25   $198.30  
  Purchase #6 $53.80   11.186%   $59.8181   $59.82   $59.80   $59.80  
  Purchase #7 $183.74   9.690%   $201.5444   $201.54   $201.55   $201.50  
  7 purchase totals = $867.64       $940.6060   $940.61   $940.55   $940.60