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	$93.54	11.734%	$104.516	$104.52	$104.50	$104.50
Purchase #2	$176.46	8.556%	$191.5579	$191.56	$191.55	$191.60
Purchase #3	$221.63	7.801%	$238.9194	$238.92	$238.90	$238.90
Purchase #4	$57.45	5.608%	$60.6718	$60.67	$60.65	$60.70
Purchase #5	$123.80	6.441%	$131.774	$131.77	$131.75	$131.80
Purchase #6	$54.51	7.547%	$58.6239	$58.62	$58.60	$58.60
Purchase #7	$49.69	11.353%	$55.3313	$55.33	$55.35	$55.30
7 purchase totals =	$777.08		$841.3943	$841.39	$841.30	$841.40