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 $186.27   4.202%   $194.0971   $194.10   $194.10   $194.10  
  Purchase #2 $212.28   11.527%   $236.7495   $236.75   $236.75   $236.70  
  Purchase #3 $96.84   10.517%   $107.0247   $107.02   $107.00   $107.00  
  Purchase #4 $210.29   7.420%   $225.8935   $225.89   $225.90   $225.90  
  Purchase #5 $8.47   13.229%   $9.5905   $9.59   $9.60   $9.60  
  Purchase #6 $25.46   10.524%   $28.1394   $28.14   $28.15   $28.10  
  Purchase #7 $120.38   8.487%   $130.5967   $130.60   $130.60   $130.60  
  7 purchase totals = $859.99       $932.0914   $932.09   $932.10   $932.00