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 $208.65   12.455%   $234.6374   $234.64   $234.65   $234.60  
  Purchase #2 $202.67   11.484%   $225.9446   $225.94   $225.95   $225.90  
  Purchase #3 $169.83   7.874%   $183.2024   $183.20   $183.20   $183.20  
  Purchase #4 $167.42   12.673%   $188.6371   $188.64   $188.65   $188.60  
  Purchase #5 $59.26   5.361%   $62.4369   $62.44   $62.45   $62.40  
  Purchase #6 $60.50   5.164%   $63.6242   $63.62   $63.60   $63.60  
  Purchase #7 $243.97   8.428%   $264.5318   $264.53   $264.55   $264.50  
  7 purchase totals = $1,112.30       $1,223.0144   $1,223.01   $1,223.05   $1,222.80