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	$104.38	6.745%	$111.4204	$111.42	$111.40	$111.40
Purchase #2	$89.79	12.240%	$100.7803	$100.78	$100.80	$100.80
Purchase #3	$246.94	9.204%	$269.6684	$269.67	$269.65	$269.70
Purchase #4	$133.58	9.111%	$145.7505	$145.75	$145.75	$145.80
Purchase #5	$10.49	12.134%	$11.7629	$11.76	$11.75	$11.80
Purchase #6	$72.37	3.235%	$74.7112	$74.71	$74.70	$74.70
Purchase #7	$33.80	3.597%	$35.0158	$35.02	$35.00	$35.00
7 purchase totals =	$691.35		$749.1095	$749.11	$749.05	$749.20