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 $250.98   8.679%   $272.7626   $272.76   $272.75   $272.80  
  Purchase #2 $173.47   11.303%   $193.0773   $193.08   $193.10   $193.10  
  Purchase #3 $48.48   12.842%   $54.7058   $54.71   $54.70   $54.70  
  Purchase #4 $125.30   6.650%   $133.6325   $133.63   $133.65   $133.60  
  Purchase #5 $233.46   8.685%   $253.736   $253.74   $253.75   $253.70  
  Purchase #6 $114.74   3.813%   $119.115   $119.12   $119.10   $119.10  
  Purchase #7 $73.66   11.544%   $82.1633   $82.16   $82.15   $82.20  
  7 purchase totals = $1,020.09       $1,109.1925   $1,109.20   $1,109.20   $1,109.20