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	$80.67	10.820%	$89.3985	$89.40	$89.40	$89.40
Purchase #2	$117.43	10.261%	$129.4795	$129.48	$129.50	$129.50
Purchase #3	$90.78	10.155%	$99.9987	$100.00	$100.00	$100.00
Purchase #4	$148.88	7.547%	$160.116	$160.12	$160.10	$160.10
Purchase #5	$28.95	5.565%	$30.5611	$30.56	$30.55	$30.60
Purchase #6	$158.30	9.351%	$173.1026	$173.10	$173.10	$173.10
Purchase #7	$129.71	13.828%	$147.6463	$147.65	$147.65	$147.60
7 purchase totals =	$754.72		$830.3027	$830.31	$830.30	$830.30