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 $86.52   13.271%   $98.0021   $98.00   $98.00   $98.00  
  Purchase #2 $65.81   8.233%   $71.2281   $71.23   $71.25   $71.20  
  Purchase #3 $73.78   8.600%   $80.1251   $80.13   $80.15   $80.10  
  Purchase #4 $159.62   4.123%   $166.2011   $166.20   $166.20   $166.20  
  Purchase #5 $47.33   9.581%   $51.8647   $51.86   $51.85   $51.90  
  Purchase #6 $137.61   10.297%   $151.7797   $151.78   $151.80   $151.80  
  Purchase #7 $207.28   11.334%   $230.7731   $230.77   $230.75   $230.80  
  7 purchase totals = $777.95       $849.9739   $849.97   $850.00   $850.00