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	$136.74	3.482%	$141.5013	$141.50	$141.50	$141.50
Purchase #2	$47.87	9.195%	$52.2716	$52.27	$52.25	$52.30
Purchase #3	$67.98	4.820%	$71.2566	$71.26	$71.25	$71.30
Purchase #4	$47.38	11.182%	$52.678	$52.68	$52.70	$52.70
Purchase #5	$193.72	5.475%	$204.3262	$204.33	$204.35	$204.30
Purchase #6	$101.82	9.568%	$111.5621	$111.56	$111.55	$111.60
Purchase #7	$49.84	10.280%	$54.9636	$54.96	$54.95	$55.00
7 purchase totals =	$645.35		$688.5594	$688.56	$688.55	$688.70