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 $226.94   8.373%   $245.9417   $245.94   $245.95   $245.90  
  Purchase #2 $38.93   5.827%   $41.1985   $41.20   $41.20   $41.20  
  Purchase #3 $104.66   12.325%   $117.5593   $117.56   $117.55   $117.60  
  Purchase #4 $169.79   3.230%   $175.2742   $175.27   $175.25   $175.30  
  Purchase #5 $144.77   13.377%   $164.1359   $164.14   $164.15   $164.10  
  Purchase #6 $229.75   13.211%   $260.1023   $260.10   $260.10   $260.10  
  Purchase #7 $34.94   10.420%   $38.5807   $38.58   $38.60   $38.60  
  7 purchase totals = $949.78       $1,042.7926   $1,042.79   $1,042.80   $1,042.80