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	$91.26	10.135%	$100.5092	$100.51	$100.50	$100.50
Purchase #2	$242.48	6.581%	$258.4376	$258.44	$258.45	$258.40
Purchase #3	$82.60	8.423%	$89.5574	$89.56	$89.55	$89.60
Purchase #4	$165.56	5.323%	$174.3728	$174.37	$174.35	$174.40
Purchase #5	$243.88	8.848%	$265.4585	$265.46	$265.45	$265.50
Purchase #6	$58.36	4.635%	$61.065	$61.07	$61.05	$61.10
Purchase #7	$238.32	5.447%	$251.3013	$251.30	$251.30	$251.30
7 purchase totals =	$1,122.46		$1,200.7018	$1,200.71	$1,200.65	$1,200.80