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	$49.58	13.280%	$56.1642	$56.16	$56.15	$56.20
Purchase #2	$27.38	7.213%	$29.3549	$29.35	$29.35	$29.40
Purchase #3	$222.56	9.420%	$243.5252	$243.53	$243.55	$243.50
Purchase #4	$91.98	13.607%	$104.4957	$104.50	$104.50	$104.50
Purchase #5	$55.72	8.801%	$60.6239	$60.62	$60.60	$60.60
Purchase #6	$171.91	6.473%	$183.0377	$183.04	$183.05	$183.00
Purchase #7	$61.83	13.722%	$70.3143	$70.31	$70.30	$70.30
7 purchase totals =	$680.96		$747.5159	$747.51	$747.50	$747.50