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 $98.99   5.808%   $104.7393   $104.74   $104.75   $104.70  
  Purchase #2 $33.25   5.324%   $35.0202   $35.02   $35.00   $35.00  
  Purchase #3 $9.91   7.201%   $10.6236   $10.62   $10.60   $10.60  
  Purchase #4 $248.38   7.190%   $266.2385   $266.24   $266.25   $266.20  
  Purchase #5 $78.37   10.789%   $86.8253   $86.83   $86.85   $86.80  
  Purchase #6 $181.36   10.751%   $200.858   $200.86   $200.85   $200.90  
  Purchase #7 $25.41   3.869%   $26.3931   $26.39   $26.40   $26.40  
  7 purchase totals = $675.67       $730.6980   $730.70   $730.70   $730.60