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 $87.94   6.509%   $93.664   $93.66   $93.65   $93.70  
  Purchase #2 $140.73   4.579%   $147.174   $147.17   $147.15   $147.20  
  Purchase #3 $54.37   9.216%   $59.3807   $59.38   $59.40   $59.40  
  Purchase #4 $86.61   8.189%   $93.7025   $93.70   $93.70   $93.70  
  Purchase #5 $94.73   3.518%   $98.0626   $98.06   $98.05   $98.10  
  Purchase #6 $250.57   8.180%   $271.0666   $271.07   $271.05   $271.10  
  Purchase #7 $235.84   12.867%   $266.1855   $266.19   $266.20   $266.20  
  7 purchase totals = $950.79       $1,029.2359   $1,029.23   $1,029.20   $1,029.40