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 $169.61   8.243%   $183.591   $183.59   $183.60   $183.60  
  Purchase #2 $86.69   6.751%   $92.5424   $92.54   $92.55   $92.50  
  Purchase #3 $108.96   7.155%   $116.7561   $116.76   $116.75   $116.80  
  Purchase #4 $50.68   11.833%   $56.677   $56.68   $56.70   $56.70  
  Purchase #5 $130.42   8.153%   $141.0531   $141.05   $141.05   $141.10  
  Purchase #6 $168.45   5.232%   $177.2633   $177.26   $177.25   $177.30  
  Purchase #7 $241.73   3.549%   $250.309   $250.31   $250.30   $250.30  
  7 purchase totals = $956.54       $1,018.1919   $1,018.19   $1,018.20   $1,018.30