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	$63.44	6.608%	$67.6321	$67.63	$67.65	$67.60
Purchase #2	$88.72	10.289%	$97.8484	$97.85	$97.85	$97.80
Purchase #3	$226.28	7.711%	$243.7285	$243.73	$243.75	$243.70
Purchase #4	$175.54	8.298%	$190.1063	$190.11	$190.10	$190.10
Purchase #5	$75.41	4.531%	$78.8268	$78.83	$78.85	$78.80
Purchase #6	$48.28	9.849%	$53.0351	$53.04	$53.05	$53.00
Purchase #7	$138.91	9.684%	$152.362	$152.36	$152.35	$152.40
7 purchase totals =	$816.58		$883.5392	$883.55	$883.60	$883.40