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 $239.67   13.233%   $271.3855   $271.39   $271.40   $271.40  
  Purchase #2 $181.94   10.603%   $201.2311   $201.23   $201.25   $201.20  
  Purchase #3 $41.71   12.642%   $46.983   $46.98   $47.00   $47.00  
  Purchase #4 $208.73   13.402%   $236.704   $236.70   $236.70   $236.70  
  Purchase #5 $135.77   7.624%   $146.1211   $146.12   $146.10   $146.10  
  Purchase #6 $68.64   9.536%   $75.1855   $75.19   $75.20   $75.20  
  Purchase #7 $92.96   6.303%   $98.8193   $98.82   $98.80   $98.80  
  7 purchase totals = $969.42       $1,076.4295   $1,076.43   $1,076.45   $1,076.40