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	$72.39	10.322%	$79.8621	$79.86	$79.85	$79.90
Purchase #2	$89.99	5.144%	$94.6191	$94.62	$94.60	$94.60
Purchase #3	$241.41	12.201%	$270.8644	$270.86	$270.85	$270.90
Purchase #4	$34.28	9.567%	$37.5596	$37.56	$37.55	$37.60
Purchase #5	$91.77	9.595%	$100.5753	$100.58	$100.60	$100.60
Purchase #6	$16.56	6.221%	$17.5902	$17.59	$17.60	$17.60
Purchase #7	$135.96	7.517%	$146.1801	$146.18	$146.20	$146.20
7 purchase totals =	$682.36		$747.2508	$747.25	$747.25	$747.40