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	$128.95	12.165%	$144.6368	$144.64	$144.65	$144.60
Purchase #2	$231.91	3.501%	$240.0292	$240.03	$240.05	$240.00
Purchase #3	$42.39	9.183%	$46.2827	$46.28	$46.30	$46.30
Purchase #4	$58.86	11.220%	$65.4641	$65.46	$65.45	$65.50
Purchase #5	$98.53	8.170%	$106.5799	$106.58	$106.60	$106.60
Purchase #6	$40.88	12.418%	$45.9565	$45.96	$45.95	$46.00
Purchase #7	$9.33	12.762%	$10.5207	$10.52	$10.50	$10.50
7 purchase totals =	$610.85		$659.4699	$659.47	$659.50	$659.50