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	$49.38	6.353%	$52.5171	$52.52	$52.50	$52.50
Purchase #2	$110.82	6.272%	$117.7706	$117.77	$117.75	$117.80
Purchase #3	$180.65	4.828%	$189.3718	$189.37	$189.35	$189.40
Purchase #4	$71.92	9.261%	$78.5805	$78.58	$78.60	$78.60
Purchase #5	$110.83	6.767%	$118.3299	$118.33	$118.35	$118.30
Purchase #6	$134.36	3.383%	$138.9054	$138.91	$138.90	$138.90
Purchase #7	$90.72	10.445%	$100.1957	$100.20	$100.20	$100.20
7 purchase totals =	$748.68		$795.6710	$795.68	$795.65	$795.70