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	$152.68	12.109%	$171.168	$171.17	$171.15	$171.20
Purchase #2	$51.91	4.866%	$54.4359	$54.44	$54.45	$54.40
Purchase #3	$168.79	5.770%	$178.5292	$178.53	$178.55	$178.50
Purchase #4	$148.82	12.140%	$166.8867	$166.89	$166.90	$166.90
Purchase #5	$96.91	8.113%	$104.7723	$104.77	$104.75	$104.80
Purchase #6	$85.70	9.398%	$93.7541	$93.75	$93.75	$93.80
Purchase #7	$61.66	6.176%	$65.4681	$65.47	$65.45	$65.50
7 purchase totals =	$766.47		$835.0143	$835.02	$835.00	$835.10