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 $69.30   9.717%   $76.0339   $76.03   $76.05   $76.00  
  Purchase #2 $56.99   6.396%   $60.6351   $60.64   $60.65   $60.60  
  Purchase #3 $22.43   6.801%   $23.9555   $23.96   $23.95   $24.00  
  Purchase #4 $125.34   13.603%   $142.39   $142.39   $142.40   $142.40  
  Purchase #5 $244.91   10.503%   $270.6329   $270.63   $270.65   $270.60  
  Purchase #6 $91.49   12.770%   $103.1733   $103.17   $103.15   $103.20  
  Purchase #7 $39.80   5.842%   $42.1251   $42.13   $42.15   $42.10  
  7 purchase totals = $650.26       $718.9458   $718.95   $719.00   $718.90