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 $92.48   6.118%   $98.1379   $98.14   $98.15   $98.10  
  Purchase #2 $97.80   6.564%   $104.2196   $104.22   $104.20   $104.20  
  Purchase #3 $128.27   6.633%   $136.7781   $136.78   $136.80   $136.80  
  Purchase #4 $217.58   7.493%   $233.8833   $233.88   $233.90   $233.90  
  Purchase #5 $126.44   10.842%   $140.1486   $140.15   $140.15   $140.10  
  Purchase #6 $97.69   5.769%   $103.3257   $103.33   $103.35   $103.30  
  Purchase #7 $34.96   10.750%   $38.7182   $38.72   $38.70   $38.70  
  7 purchase totals = $795.22       $855.2114   $855.22   $855.25   $855.10