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	$91.27	12.648%	$102.8138	$102.81	$102.80	$102.80
Purchase #2	$70.96	12.523%	$79.8463	$79.85	$79.85	$79.80
Purchase #3	$151.92	5.483%	$160.2498	$160.25	$160.25	$160.20
Purchase #4	$62.30	8.557%	$67.631	$67.63	$67.65	$67.60
Purchase #5	$243.97	9.861%	$268.0279	$268.03	$268.05	$268.00
Purchase #6	$30.59	10.565%	$33.8218	$33.82	$33.80	$33.80
Purchase #7	$48.34	12.420%	$54.3438	$54.34	$54.35	$54.30
7 purchase totals =	$699.35		$766.7344	$766.73	$766.75	$766.50