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	$75.93	13.629%	$86.2785	$86.28	$86.30	$86.30
Purchase #2	$209.76	3.607%	$217.326	$217.33	$217.35	$217.30
Purchase #3	$80.91	10.767%	$89.6216	$89.62	$89.60	$89.60
Purchase #4	$63.59	9.326%	$69.5204	$69.52	$69.50	$69.50
Purchase #5	$149.36	10.361%	$164.8352	$164.84	$164.85	$164.80
Purchase #6	$127.57	7.581%	$137.2411	$137.24	$137.25	$137.20
Purchase #7	$194.28	10.159%	$214.0169	$214.02	$214.00	$214.00
7 purchase totals =	$901.40		$978.8397	$978.85	$978.85	$978.70