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 $54.91   9.617%   $60.1907   $60.19   $60.20   $60.20  
  Purchase #2 $90.98   3.855%   $94.4873   $94.49   $94.50   $94.50  
  Purchase #3 $94.48   9.230%   $103.2005   $103.20   $103.20   $103.20  
  Purchase #4 $63.79   6.699%   $68.0633   $68.06   $68.05   $68.10  
  Purchase #5 $65.79   4.420%   $68.6979   $68.70   $68.70   $68.70  
  Purchase #6 $51.76   6.219%   $54.979   $54.98   $55.00   $55.00  
  Purchase #7 $211.28   12.681%   $238.0724   $238.07   $238.05   $238.10  
  7 purchase totals = $632.99       $687.6911   $687.69   $687.70   $687.80