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	$246.77	12.729%	$278.1814	$278.18	$278.20	$278.20
Purchase #2	$49.91	6.306%	$53.0573	$53.06	$53.05	$53.10
Purchase #3	$140.76	5.212%	$148.0964	$148.10	$148.10	$148.10
Purchase #4	$223.65	10.728%	$247.6432	$247.64	$247.65	$247.60
Purchase #5	$78.29	13.848%	$89.1316	$89.13	$89.15	$89.10
Purchase #6	$55.67	7.853%	$60.0418	$60.04	$60.05	$60.00
Purchase #7	$185.81	5.706%	$196.4123	$196.41	$196.40	$196.40
7 purchase totals =	$980.86		$1,072.5640	$1,072.56	$1,072.60	$1,072.50