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	$46.93	8.263%	$50.8078	$50.81	$50.80	$50.80
Purchase #2	$111.62	6.835%	$119.2492	$119.25	$119.25	$119.20
Purchase #3	$17.67	4.277%	$18.4257	$18.43	$18.45	$18.40
Purchase #4	$91.27	8.722%	$99.2306	$99.23	$99.25	$99.20
Purchase #5	$71.62	11.845%	$80.1034	$80.10	$80.10	$80.10
Purchase #6	$140.85	5.250%	$148.2446	$148.24	$148.25	$148.20
Purchase #7	$139.43	12.164%	$156.3903	$156.39	$156.40	$156.40
7 purchase totals =	$619.39		$672.4516	$672.45	$672.50	$672.30