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 $89.28   7.561%   $96.0305   $96.03   $96.05   $96.00  
  Purchase #2 $57.84   4.226%   $60.2843   $60.28   $60.30   $60.30  
  Purchase #3 $194.82   10.732%   $215.7281   $215.73   $215.75   $215.70  
  Purchase #4 $23.59   3.484%   $24.4119   $24.41   $24.40   $24.40  
  Purchase #5 $31.50   9.425%   $34.4689   $34.47   $34.45   $34.50  
  Purchase #6 $192.77   8.350%   $208.8663   $208.87   $208.85   $208.90  
  Purchase #7 $117.79   13.227%   $133.3701   $133.37   $133.35   $133.40  
  7 purchase totals = $707.59       $773.1601   $773.16   $773.15   $773.20