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	$159.86	12.314%	$179.5452	$179.55	$179.55	$179.50
Purchase #2	$87.37	13.585%	$99.2392	$99.24	$99.25	$99.20
Purchase #3	$20.41	6.231%	$21.6817	$21.68	$21.70	$21.70
Purchase #4	$220.69	12.131%	$247.4619	$247.46	$247.45	$247.50
Purchase #5	$239.76	10.432%	$264.7718	$264.77	$264.75	$264.80
Purchase #6	$120.55	7.264%	$129.3068	$129.31	$129.30	$129.30
Purchase #7	$117.25	12.499%	$131.9051	$131.91	$131.90	$131.90
7 purchase totals =	$965.89		$1,073.9117	$1,073.92	$1,073.90	$1,073.90