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	$108.29	4.149%	$112.783	$112.78	$112.80	$112.80
Purchase #2	$52.36	9.553%	$57.362	$57.36	$57.35	$57.40
Purchase #3	$37.31	13.570%	$42.373	$42.37	$42.35	$42.40
Purchase #4	$198.25	12.618%	$223.2652	$223.27	$223.25	$223.30
Purchase #5	$35.80	8.354%	$38.7907	$38.79	$38.80	$38.80
Purchase #6	$13.30	9.371%	$14.5463	$14.55	$14.55	$14.50
Purchase #7	$183.42	8.394%	$198.8163	$198.82	$198.80	$198.80
7 purchase totals =	$628.73		$687.9365	$687.94	$687.90	$688.00