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 $112.49   12.767%   $126.8516   $126.85   $126.85   $126.90  
  Purchase #2 $23.31   5.103%   $24.4995   $24.50   $24.50   $24.50  
  Purchase #3 $18.36   13.575%   $20.8524   $20.85   $20.85   $20.90  
  Purchase #4 $62.92   9.563%   $68.937   $68.94   $68.95   $68.90  
  Purchase #5 $98.64   6.691%   $105.24   $105.24   $105.25   $105.20  
  Purchase #6 $181.72   6.198%   $192.983   $192.98   $193.00   $193.00  
  Purchase #7 $235.63   3.155%   $243.0641   $243.06   $243.05   $243.10  
  7 purchase totals = $733.07       $782.4276   $782.42   $782.45   $782.50