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	$200.49	3.657%	$207.8219	$207.82	$207.80	$207.80
Purchase #2	$152.91	6.501%	$162.8507	$162.85	$162.85	$162.90
Purchase #3	$184.46	13.510%	$209.3805	$209.38	$209.40	$209.40
Purchase #4	$16.56	8.588%	$17.9822	$17.98	$18.00	$18.00
Purchase #5	$158.58	10.378%	$175.0374	$175.04	$175.05	$175.00
Purchase #6	$206.72	7.567%	$222.3625	$222.36	$222.35	$222.40
Purchase #7	$6.89	12.492%	$7.7507	$7.75	$7.75	$7.80
7 purchase totals =	$926.61		$1,003.1859	$1,003.18	$1,003.20	$1,003.30