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	$42.58	12.259%	$47.7999	$47.80	$47.80	$47.80
Purchase #2	$134.60	7.801%	$145.1001	$145.10	$145.10	$145.10
Purchase #3	$142.93	6.838%	$152.7036	$152.70	$152.70	$152.70
Purchase #4	$244.62	3.548%	$253.2991	$253.30	$253.30	$253.30
Purchase #5	$120.94	6.337%	$128.604	$128.60	$128.60	$128.60
Purchase #6	$234.55	10.121%	$258.2888	$258.29	$258.30	$258.30
Purchase #7	$172.84	13.864%	$196.8025	$196.80	$196.80	$196.80
7 purchase totals =	$1,093.06		$1,182.5980	$1,182.59	$1,182.60	$1,182.60