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	$18.55	10.453%	$20.489	$20.49	$20.50	$20.50
Purchase #2	$42.92	12.355%	$48.2228	$48.22	$48.20	$48.20
Purchase #3	$155.37	5.826%	$164.4219	$164.42	$164.40	$164.40
Purchase #4	$109.61	3.107%	$113.0156	$113.02	$113.00	$113.00
Purchase #5	$92.42	7.219%	$99.0918	$99.09	$99.10	$99.10
Purchase #6	$238.66	13.602%	$271.1225	$271.12	$271.10	$271.10
Purchase #7	$141.61	7.860%	$152.7405	$152.74	$152.75	$152.70
7 purchase totals =	$799.14		$869.1041	$869.10	$869.05	$869.00