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	$65.57	8.370%	$71.0582	$71.06	$71.05	$71.10
Purchase #2	$122.65	3.850%	$127.372	$127.37	$127.35	$127.40
Purchase #3	$38.39	12.323%	$43.1208	$43.12	$43.10	$43.10
Purchase #4	$247.63	8.815%	$269.4586	$269.46	$269.45	$269.50
Purchase #5	$49.89	6.147%	$52.9567	$52.96	$52.95	$53.00
Purchase #6	$218.99	11.518%	$244.2133	$244.21	$244.20	$244.20
Purchase #7	$167.97	13.762%	$191.086	$191.09	$191.10	$191.10
7 purchase totals =	$911.09		$999.2656	$999.27	$999.20	$999.40