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	$107.42	12.407%	$120.7476	$120.75	$120.75	$120.70
Purchase #2	$244.71	10.788%	$271.1093	$271.11	$271.10	$271.10
Purchase #3	$221.57	9.393%	$242.3821	$242.38	$242.40	$242.40
Purchase #4	$78.63	4.460%	$82.1369	$82.14	$82.15	$82.10
Purchase #5	$97.69	13.841%	$111.2113	$111.21	$111.20	$111.20
Purchase #6	$101.31	11.814%	$113.2788	$113.28	$113.30	$113.30
Purchase #7	$169.77	5.467%	$179.0513	$179.05	$179.05	$179.10
7 purchase totals =	$1,021.10		$1,119.9173	$1,119.92	$1,119.95	$1,119.90