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	$78.88	11.322%	$87.8108	$87.81	$87.80	$87.80
Purchase #2	$242.32	10.792%	$268.4712	$268.47	$268.45	$268.50
Purchase #3	$140.93	8.449%	$152.8372	$152.84	$152.85	$152.80
Purchase #4	$80.34	12.467%	$90.356	$90.36	$90.35	$90.40
Purchase #5	$171.42	4.639%	$179.3722	$179.37	$179.35	$179.40
Purchase #6	$18.26	13.670%	$20.7561	$20.76	$20.75	$20.80
Purchase #7	$12.81	5.811%	$13.5544	$13.55	$13.55	$13.60
7 purchase totals =	$744.96		$813.1579	$813.16	$813.10	$813.30