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	$153.27	5.642%	$161.9175	$161.92	$161.90	$161.90
Purchase #2	$170.34	4.736%	$178.4073	$178.41	$178.40	$178.40
Purchase #3	$85.82	3.262%	$88.6194	$88.62	$88.60	$88.60
Purchase #4	$210.68	10.835%	$233.5072	$233.51	$233.50	$233.50
Purchase #5	$61.79	7.851%	$66.6411	$66.64	$66.65	$66.60
Purchase #6	$98.73	13.110%	$111.6735	$111.67	$111.65	$111.70
Purchase #7	$120.38	6.262%	$127.9182	$127.92	$127.90	$127.90
7 purchase totals =	$901.01		$968.6842	$968.69	$968.60	$968.60