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 $94.44   9.660%   $103.5629   $103.56   $103.55   $103.60  
  Purchase #2 $25.34   3.547%   $26.2388   $26.24   $26.25   $26.20  
  Purchase #3 $198.39   7.267%   $212.807   $212.81   $212.80   $212.80  
  Purchase #4 $244.77   11.396%   $272.664   $272.66   $272.65   $272.70  
  Purchase #5 $90.82   11.696%   $101.4423   $101.44   $101.45   $101.40  
  Purchase #6 $63.63   11.399%   $70.8832   $70.88   $70.90   $70.90  
  Purchase #7 $216.67   7.678%   $233.3059   $233.31   $233.30   $233.30  
  7 purchase totals = $934.06       $1,020.9041   $1,020.90   $1,020.90   $1,020.90