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 $69.95   13.302%   $79.2547   $79.25   $79.25   $79.30  
  Purchase #2 $95.28   4.586%   $99.6495   $99.65   $99.65   $99.60  
  Purchase #3 $122.25   3.450%   $126.4676   $126.47   $126.45   $126.50  
  Purchase #4 $160.33   8.799%   $174.4374   $174.44   $174.45   $174.40  
  Purchase #5 $240.73   8.470%   $261.1198   $261.12   $261.10   $261.10  
  Purchase #6 $200.97   9.557%   $220.1767   $220.18   $220.20   $220.20  
  Purchase #7 $98.27   3.523%   $101.7321   $101.73   $101.75   $101.70  
  7 purchase totals = $987.78       $1,062.8378   $1,062.84   $1,062.85   $1,062.80