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 $214.42   12.401%   $241.0102   $241.01   $241.00   $241.00  
  Purchase #2 $25.51   4.680%   $26.7039   $26.70   $26.70   $26.70  
  Purchase #3 $111.62   5.159%   $117.3785   $117.38   $117.40   $117.40  
  Purchase #4 $164.95   8.872%   $179.5844   $179.58   $179.60   $179.60  
  Purchase #5 $94.39   7.412%   $101.3862   $101.39   $101.40   $101.40  
  Purchase #6 $180.66   5.758%   $191.0624   $191.06   $191.05   $191.10  
  Purchase #7 $227.39   7.119%   $243.5779   $243.58   $243.60   $243.60  
  7 purchase totals = $1,018.94       $1,100.7035   $1,100.70   $1,100.75   $1,100.80