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 $247.36   6.152%   $262.5776   $262.58   $262.60   $262.60  
  Purchase #2 $183.77   4.347%   $191.7585   $191.76   $191.75   $191.80  
  Purchase #3 $18.37   12.358%   $20.6402   $20.64   $20.65   $20.60  
  Purchase #4 $76.68   13.412%   $86.9643   $86.96   $86.95   $87.00  
  Purchase #5 $94.56   3.358%   $97.7353   $97.74   $97.75   $97.70  
  Purchase #6 $225.83   3.363%   $233.4247   $233.42   $233.40   $233.40  
  Purchase #7 $29.66   4.656%   $31.041   $31.04   $31.05   $31.00  
  7 purchase totals = $876.23       $924.1416   $924.14   $924.15   $924.10