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	$200.35	13.766%	$227.9302	$227.93	$227.95	$227.90
Purchase #2	$235.31	5.557%	$248.3862	$248.39	$248.40	$248.40
Purchase #3	$56.54	8.167%	$61.1576	$61.16	$61.15	$61.20
Purchase #4	$94.31	5.498%	$99.4952	$99.50	$99.50	$99.50
Purchase #5	$148.33	7.867%	$159.9991	$160.00	$160.00	$160.00
Purchase #6	$136.55	8.582%	$148.2687	$148.27	$148.25	$148.30
Purchase #7	$125.89	7.119%	$134.8521	$134.85	$134.85	$134.90
7 purchase totals =	$997.28		$1,080.0891	$1,080.10	$1,080.10	$1,080.20