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 $143.97   6.663%   $153.5627   $153.56   $153.55   $153.60  
  Purchase #2 $149.67   11.710%   $167.1964   $167.20   $167.20   $167.20  
  Purchase #3 $113.80   13.797%   $129.501   $129.50   $129.50   $129.50  
  Purchase #4 $194.54   11.408%   $216.7331   $216.73   $216.75   $216.70  
  Purchase #5 $47.94   6.141%   $50.884   $50.88   $50.90   $50.90  
  Purchase #6 $239.36   3.348%   $247.3738   $247.37   $247.35   $247.40  
  Purchase #7 $210.65   12.106%   $236.1513   $236.15   $236.15   $236.20  
  7 purchase totals = $1,099.93       $1,201.4023   $1,201.39   $1,201.40   $1,201.50