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	$91.54	8.292%	$99.1305	$99.13	$99.15	$99.10
Purchase #2	$72.80	10.103%	$80.155	$80.16	$80.15	$80.20
Purchase #3	$113.38	9.152%	$123.7565	$123.76	$123.75	$123.80
Purchase #4	$25.34	12.542%	$28.5181	$28.52	$28.50	$28.50
Purchase #5	$78.38	12.615%	$88.2676	$88.27	$88.25	$88.30
Purchase #6	$226.27	4.722%	$236.9545	$236.95	$236.95	$237.00
Purchase #7	$92.41	3.639%	$95.7728	$95.77	$95.75	$95.80
7 purchase totals =	$700.12		$752.5550	$752.56	$752.50	$752.70