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 $151.31   9.209%   $165.2441   $165.24   $165.25   $165.20  
  Purchase #2 $104.35   10.555%   $115.3641   $115.36   $115.35   $115.40  
  Purchase #3 $25.70   11.283%   $28.5997   $28.60   $28.60   $28.60  
  Purchase #4 $115.57   9.177%   $126.1759   $126.18   $126.20   $126.20  
  Purchase #5 $23.56   12.626%   $26.5347   $26.53   $26.55   $26.50  
  Purchase #6 $250.42   4.121%   $260.7398   $260.74   $260.75   $260.70  
  Purchase #7 $30.67   10.671%   $33.9428   $33.94   $33.95   $33.90  
  7 purchase totals = $701.58       $756.6011   $756.59   $756.65   $756.50