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	$134.83	12.431%	$151.5907	$151.59	$151.60	$151.60
Purchase #2	$81.87	11.689%	$91.4398	$91.44	$91.45	$91.40
Purchase #3	$230.75	12.797%	$260.2791	$260.28	$260.30	$260.30
Purchase #4	$213.36	11.140%	$237.1283	$237.13	$237.15	$237.10
Purchase #5	$250.81	13.297%	$284.1602	$284.16	$284.15	$284.20
Purchase #6	$105.48	10.573%	$116.6324	$116.63	$116.65	$116.60
Purchase #7	$82.63	9.663%	$90.6145	$90.61	$90.60	$90.60
7 purchase totals =	$1,099.73		$1,231.8450	$1,231.84	$1,231.90	$1,231.80