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	$184.62	3.729%	$191.5045	$191.50	$191.50	$191.50
Purchase #2	$248.40	4.209%	$258.8552	$258.86	$258.85	$258.90
Purchase #3	$166.95	7.860%	$180.0723	$180.07	$180.05	$180.10
Purchase #4	$30.67	7.180%	$32.8721	$32.87	$32.85	$32.90
Purchase #5	$68.88	5.224%	$72.4783	$72.48	$72.50	$72.50
Purchase #6	$66.39	13.453%	$75.3214	$75.32	$75.30	$75.30
Purchase #7	$236.51	13.853%	$269.2737	$269.27	$269.25	$269.30
7 purchase totals =	$1,002.42		$1,080.3775	$1,080.37	$1,080.30	$1,080.50