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	$66.70	6.236%	$70.8594	$70.86	$70.85	$70.90
Purchase #2	$193.68	9.728%	$212.5212	$212.52	$212.50	$212.50
Purchase #3	$66.34	8.345%	$71.8761	$71.88	$71.90	$71.90
Purchase #4	$205.59	8.626%	$223.3242	$223.32	$223.30	$223.30
Purchase #5	$136.39	8.764%	$148.3432	$148.34	$148.35	$148.30
Purchase #6	$94.71	9.259%	$103.4792	$103.48	$103.50	$103.50
Purchase #7	$9.98	10.285%	$11.0064	$11.01	$11.00	$11.00
7 purchase totals =	$773.39		$841.4097	$841.41	$841.40	$841.40