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	$80.91	11.425%	$90.154	$90.15	$90.15	$90.20
Purchase #2	$177.40	11.231%	$197.3238	$197.32	$197.30	$197.30
Purchase #3	$85.47	10.368%	$94.3315	$94.33	$94.35	$94.30
Purchase #4	$48.37	10.456%	$53.4276	$53.43	$53.45	$53.40
Purchase #5	$248.43	11.236%	$276.3436	$276.34	$276.35	$276.30
Purchase #6	$21.70	8.349%	$23.5117	$23.51	$23.50	$23.50
Purchase #7	$85.82	6.589%	$91.4747	$91.47	$91.45	$91.50
7 purchase totals =	$748.10		$826.5669	$826.55	$826.55	$826.50