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 $95.45   9.753%   $104.7592   $104.76   $104.75   $104.80  
  Purchase #2 $76.65   13.424%   $86.9395   $86.94   $86.95   $86.90  
  Purchase #3 $145.69   6.427%   $155.0535   $155.05   $155.05   $155.10  
  Purchase #4 $119.27   11.105%   $132.5149   $132.51   $132.50   $132.50  
  Purchase #5 $90.37   12.651%   $101.8027   $101.80   $101.80   $101.80  
  Purchase #6 $188.62   10.624%   $208.659   $208.66   $208.65   $208.70  
  Purchase #7 $205.64   6.211%   $218.4123   $218.41   $218.40   $218.40  
  7 purchase totals = $921.69       $1,008.1411   $1,008.13   $1,008.10   $1,008.20