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	$50.63	13.495%	$57.4625	$57.46	$57.45	$57.50
Purchase #2	$45.72	13.230%	$51.7688	$51.77	$51.75	$51.80
Purchase #3	$146.51	3.813%	$152.0964	$152.10	$152.10	$152.10
Purchase #4	$130.45	10.615%	$144.2973	$144.30	$144.30	$144.30
Purchase #5	$53.73	4.469%	$56.1312	$56.13	$56.15	$56.10
Purchase #6	$102.74	13.277%	$116.3808	$116.38	$116.40	$116.40
Purchase #7	$33.70	10.336%	$37.1832	$37.18	$37.20	$37.20
7 purchase totals =	$563.48		$615.3202	$615.32	$615.35	$615.40