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 $24.54   8.506%   $26.6274   $26.63   $26.65   $26.60  
  Purchase #2 $65.94   3.849%   $68.478   $68.48   $68.50   $68.50  
  Purchase #3 $118.49   10.433%   $130.8521   $130.85   $130.85   $130.90  
  Purchase #4 $35.65   10.713%   $39.4692   $39.47   $39.45   $39.50  
  Purchase #5 $135.66   3.147%   $139.9292   $139.93   $139.95   $139.90  
  Purchase #6 $140.91   4.576%   $147.358   $147.36   $147.35   $147.40  
  Purchase #7 $42.37   8.593%   $46.0109   $46.01   $46.00   $46.00  
  7 purchase totals = $563.56       $598.7248   $598.73   $598.75   $598.80