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	$161.56	12.603%	$181.9214	$181.92	$181.90	$181.90
Purchase #2	$48.35	5.276%	$50.9009	$50.90	$50.90	$50.90
Purchase #3	$222.64	12.533%	$250.5435	$250.54	$250.55	$250.50
Purchase #4	$24.36	11.295%	$27.1115	$27.11	$27.10	$27.10
Purchase #5	$172.41	3.612%	$178.6374	$178.64	$178.65	$178.60
Purchase #6	$105.62	5.715%	$111.6562	$111.66	$111.65	$111.70
Purchase #7	$19.80	5.485%	$20.886	$20.89	$20.90	$20.90
7 purchase totals =	$754.74		$821.6569	$821.66	$821.65	$821.60