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 $134.63   12.746%   $151.7899   $151.79   $151.80   $151.80  
  Purchase #2 $215.38   9.296%   $235.4017   $235.40   $235.40   $235.40  
  Purchase #3 $208.26   12.666%   $234.6382   $234.64   $234.65   $234.60  
  Purchase #4 $155.82   13.341%   $176.6079   $176.61   $176.60   $176.60  
  Purchase #5 $96.46   10.162%   $106.2623   $106.26   $106.25   $106.30  
  Purchase #6 $20.81   3.486%   $21.5354   $21.54   $21.55   $21.50  
  Purchase #7 $71.67   8.658%   $77.8752   $77.88   $77.90   $77.90  
  7 purchase totals = $903.03       $1,004.1106   $1,004.12   $1,004.15   $1,004.10