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 $158.62   6.671%   $169.2015   $169.20   $169.20   $169.20  
  Purchase #2 $143.97   8.705%   $156.5026   $156.50   $156.50   $156.50  
  Purchase #3 $200.94   10.501%   $222.0407   $222.04   $222.05   $222.00  
  Purchase #4 $112.78   3.479%   $116.7036   $116.70   $116.70   $116.70  
  Purchase #5 $34.45   4.186%   $35.8921   $35.89   $35.90   $35.90  
  Purchase #6 $112.54   4.542%   $117.6516   $117.65   $117.65   $117.70  
  Purchase #7 $170.74   7.296%   $183.1972   $183.20   $183.20   $183.20  
  7 purchase totals = $934.04       $1,001.1893   $1,001.18   $1,001.20   $1,001.20