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	$81.34	11.822%	$90.956	$90.96	$90.95	$91.00
Purchase #2	$20.28	10.204%	$22.3494	$22.35	$22.35	$22.30
Purchase #3	$158.87	8.437%	$172.2739	$172.27	$172.25	$172.30
Purchase #4	$166.91	10.407%	$184.2803	$184.28	$184.30	$184.30
Purchase #5	$27.83	6.762%	$29.7119	$29.71	$29.70	$29.70
Purchase #6	$217.54	3.629%	$225.4345	$225.43	$225.45	$225.40
Purchase #7	$50.98	4.800%	$53.427	$53.43	$53.45	$53.40
7 purchase totals =	$723.75		$778.4330	$778.43	$778.45	$778.40