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	$234.33	5.758%	$247.8227	$247.82	$247.80	$247.80
Purchase #2	$127.98	8.853%	$139.3101	$139.31	$139.30	$139.30
Purchase #3	$220.77	9.422%	$241.5709	$241.57	$241.55	$241.60
Purchase #4	$221.41	10.591%	$244.8595	$244.86	$244.85	$244.90
Purchase #5	$40.26	13.314%	$45.6202	$45.62	$45.60	$45.60
Purchase #6	$79.65	3.502%	$82.4393	$82.44	$82.45	$82.40
Purchase #7	$199.36	11.648%	$222.5815	$222.58	$222.60	$222.60
7 purchase totals =	$1,123.76		$1,224.2042	$1,224.20	$1,224.15	$1,224.20