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 $91.98   6.739%   $98.1785   $98.18   $98.20   $98.20  
  Purchase #2 $197.47   5.759%   $208.8423   $208.84   $208.85   $208.80  
  Purchase #3 $118.38   5.298%   $124.6518   $124.65   $124.65   $124.70  
  Purchase #4 $91.87   9.734%   $100.8126   $100.81   $100.80   $100.80  
  Purchase #5 $132.28   3.513%   $136.927   $136.93   $136.95   $136.90  
  Purchase #6 $136.69   7.838%   $147.4038   $147.40   $147.40   $147.40  
  Purchase #7 $135.55   13.139%   $153.3599   $153.36   $153.35   $153.40  
  7 purchase totals = $904.22       $970.1759   $970.17   $970.20   $970.20