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 $110.47   11.243%   $122.8901   $122.89   $122.90   $122.90  
  Purchase #2 $249.74   5.805%   $264.2374   $264.24   $264.25   $264.20  
  Purchase #3 $109.57   6.396%   $116.5781   $116.58   $116.60   $116.60  
  Purchase #4 $125.95   4.189%   $131.226   $131.23   $131.25   $131.20  
  Purchase #5 $109.28   6.460%   $116.3395   $116.34   $116.35   $116.30  
  Purchase #6 $225.85   12.685%   $254.4991   $254.50   $254.50   $254.50  
  Purchase #7 $154.74   4.189%   $161.2221   $161.22   $161.20   $161.20  
  7 purchase totals = $1,085.60       $1,166.9923   $1,167.00   $1,167.05   $1,166.90