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 $216.33   11.719%   $241.6817   $241.68   $241.70   $241.70  
  Purchase #2 $150.91   4.577%   $157.8172   $157.82   $157.80   $157.80  
  Purchase #3 $113.79   5.810%   $120.4012   $120.40   $120.40   $120.40  
  Purchase #4 $68.29   7.105%   $73.142   $73.14   $73.15   $73.10  
  Purchase #5 $235.48   13.513%   $267.3004   $267.30   $267.30   $267.30  
  Purchase #6 $75.48   12.179%   $84.6727   $84.67   $84.65   $84.70  
  Purchase #7 $240.65   12.865%   $271.6096   $271.61   $271.60   $271.60  
  7 purchase totals = $1,100.93       $1,216.6248   $1,216.62   $1,216.60   $1,216.60