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	$155.69	12.642%	$175.3723	$175.37	$175.35	$175.40
Purchase #2	$42.79	8.604%	$46.4717	$46.47	$46.45	$46.50
Purchase #3	$136.47	11.218%	$151.7792	$151.78	$151.80	$151.80
Purchase #4	$244.56	8.623%	$265.6484	$265.65	$265.65	$265.60
Purchase #5	$185.65	4.757%	$194.4814	$194.48	$194.50	$194.50
Purchase #6	$242.86	5.614%	$256.4942	$256.49	$256.50	$256.50
Purchase #7	$141.43	9.343%	$154.6438	$154.64	$154.65	$154.60
7 purchase totals =	$1,149.45		$1,244.8910	$1,244.88	$1,244.90	$1,244.90