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 $176.40   8.699%   $191.745   $191.75   $191.75   $191.70  
  Purchase #2 $99.56   4.720%   $104.2592   $104.26   $104.25   $104.30  
  Purchase #3 $197.90   8.474%   $214.67   $214.67   $214.65   $214.70  
  Purchase #4 $240.83   10.854%   $266.9697   $266.97   $266.95   $267.00  
  Purchase #5 $54.53   8.831%   $59.3455   $59.35   $59.35   $59.30  
  Purchase #6 $250.47   6.624%   $267.0611   $267.06   $267.05   $267.10  
  Purchase #7 $67.56   11.303%   $75.1963   $75.20   $75.20   $75.20  
  7 purchase totals = $1,087.25       $1,179.2468   $1,179.26   $1,179.20   $1,179.30