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	$246.54	7.140%	$264.143	$264.14	$264.15	$264.10
Purchase #2	$182.35	4.221%	$190.047	$190.05	$190.05	$190.00
Purchase #3	$40.98	5.343%	$43.1696	$43.17	$43.15	$43.20
Purchase #4	$19.75	3.384%	$20.4183	$20.42	$20.40	$20.40
Purchase #5	$133.60	3.752%	$138.6127	$138.61	$138.60	$138.60
Purchase #6	$16.68	13.196%	$18.8811	$18.88	$18.90	$18.90
Purchase #7	$151.76	9.153%	$165.6506	$165.65	$165.65	$165.70
7 purchase totals =	$791.66		$840.9223	$840.92	$840.90	$840.90