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	$81.38	10.257%	$89.7271	$89.73	$89.75	$89.70
Purchase #2	$93.92	10.867%	$104.1263	$104.13	$104.15	$104.10
Purchase #3	$52.74	12.515%	$59.3404	$59.34	$59.35	$59.30
Purchase #4	$180.53	13.251%	$204.452	$204.45	$204.45	$204.50
Purchase #5	$101.88	4.494%	$106.4585	$106.46	$106.45	$106.50
Purchase #6	$19.70	13.456%	$22.3508	$22.35	$22.35	$22.40
Purchase #7	$57.67	4.428%	$60.2236	$60.22	$60.20	$60.20
7 purchase totals =	$587.82		$646.6787	$646.68	$646.70	$646.70