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 $176.28   5.104%   $185.2773   $185.28   $185.30   $185.30  
  Purchase #2 $238.68   11.263%   $265.5625   $265.56   $265.55   $265.60  
  Purchase #3 $22.45   3.658%   $23.2712   $23.27   $23.25   $23.30  
  Purchase #4 $60.86   7.444%   $65.3904   $65.39   $65.40   $65.40  
  Purchase #5 $109.41   6.411%   $116.4243   $116.42   $116.40   $116.40  
  Purchase #6 $113.46   10.663%   $125.5582   $125.56   $125.55   $125.60  
  Purchase #7 $196.81   11.636%   $219.7108   $219.71   $219.70   $219.70  
  7 purchase totals = $917.95       $1,001.1947   $1,001.19   $1,001.15   $1,001.30