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	$151.90	5.401%	$160.1041	$160.10	$160.10	$160.10
Purchase #2	$151.40	5.682%	$160.0025	$160.00	$160.00	$160.00
Purchase #3	$50.46	12.787%	$56.9123	$56.91	$56.90	$56.90
Purchase #4	$110.36	9.172%	$120.4822	$120.48	$120.50	$120.50
Purchase #5	$51.66	9.587%	$56.6126	$56.61	$56.60	$56.60
Purchase #6	$66.76	7.596%	$71.8311	$71.83	$71.85	$71.80
Purchase #7	$49.28	6.129%	$52.3004	$52.30	$52.30	$52.30
7 purchase totals =	$631.82		$678.2452	$678.23	$678.25	$678.20