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 $240.56   11.522%   $268.2773   $268.28   $268.30   $268.30  
  Purchase #2 $159.46   5.102%   $167.5956   $167.60   $167.60   $167.60  
  Purchase #3 $98.58   5.648%   $104.1478   $104.15   $104.15   $104.10  
  Purchase #4 $100.25   4.408%   $104.669   $104.67   $104.65   $104.70  
  Purchase #5 $86.92   10.186%   $95.7737   $95.77   $95.75   $95.80  
  Purchase #6 $181.79   11.319%   $202.3668   $202.37   $202.35   $202.40  
  Purchase #7 $113.43   13.413%   $128.6444   $128.64   $128.65   $128.60  
  7 purchase totals = $980.99       $1,071.4746   $1,071.48   $1,071.45   $1,071.50