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	$236.27	13.137%	$267.3088	$267.31	$267.30	$267.30
Purchase #2	$114.33	10.364%	$126.1792	$126.18	$126.20	$126.20
Purchase #3	$167.47	12.795%	$188.8978	$188.90	$188.90	$188.90
Purchase #4	$111.65	5.192%	$117.4469	$117.45	$117.45	$117.40
Purchase #5	$100.78	10.426%	$111.2873	$111.29	$111.30	$111.30
Purchase #6	$104.36	4.169%	$108.7108	$108.71	$108.70	$108.70
Purchase #7	$53.62	7.116%	$57.4356	$57.44	$57.45	$57.40
7 purchase totals =	$888.48		$977.2664	$977.28	$977.30	$977.20