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 $91.50   5.741%   $96.753   $96.75   $96.75   $96.80  
  Purchase #2 $226.55   6.203%   $240.6029   $240.60   $240.60   $240.60  
  Purchase #3 $118.37   13.578%   $134.4423   $134.44   $134.45   $134.40  
  Purchase #4 $166.39   5.290%   $175.192   $175.19   $175.20   $175.20  
  Purchase #5 $32.56   12.633%   $36.6733   $36.67   $36.65   $36.70  
  Purchase #6 $216.79   10.194%   $238.8896   $238.89   $238.90   $238.90  
  Purchase #7 $58.32   6.431%   $62.0706   $62.07   $62.05   $62.10  
  7 purchase totals = $910.48       $984.6237   $984.61   $984.60   $984.70