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	$236.39	6.872%	$252.6347	$252.63	$252.65	$252.60
Purchase #2	$40.91	11.462%	$45.5991	$45.60	$45.60	$45.60
Purchase #3	$54.81	8.687%	$59.5713	$59.57	$59.55	$59.60
Purchase #4	$233.96	12.425%	$263.0295	$263.03	$263.05	$263.00
Purchase #5	$49.76	11.810%	$55.6367	$55.64	$55.65	$55.60
Purchase #6	$39.74	7.561%	$42.7447	$42.74	$42.75	$42.70
Purchase #7	$84.75	12.303%	$95.1768	$95.18	$95.20	$95.20
7 purchase totals =	$740.32		$814.3928	$814.39	$814.45	$814.30