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	$42.81	8.142%	$46.2956	$46.30	$46.30	$46.30
Purchase #2	$46.97	13.693%	$53.4016	$53.40	$53.40	$53.40
Purchase #3	$137.73	6.520%	$146.71	$146.71	$146.70	$146.70
Purchase #4	$237.90	11.442%	$265.1205	$265.12	$265.10	$265.10
Purchase #5	$116.45	10.427%	$128.5922	$128.59	$128.60	$128.60
Purchase #6	$158.54	4.566%	$165.7789	$165.78	$165.80	$165.80
Purchase #7	$87.30	6.667%	$93.1203	$93.12	$93.10	$93.10
7 purchase totals =	$827.70		$899.0191	$899.02	$899.00	$899.00