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	$210.31	6.459%	$223.8939	$223.89	$223.90	$223.90
Purchase #2	$114.66	8.247%	$124.116	$124.12	$124.10	$124.10
Purchase #3	$70.92	12.793%	$79.9928	$79.99	$80.00	$80.00
Purchase #4	$91.34	8.693%	$99.2802	$99.28	$99.30	$99.30
Purchase #5	$171.25	12.679%	$192.9628	$192.96	$192.95	$193.00
Purchase #6	$37.80	6.826%	$40.3802	$40.38	$40.40	$40.40
Purchase #7	$213.89	9.313%	$233.8096	$233.81	$233.80	$233.80
7 purchase totals =	$910.17		$994.4355	$994.43	$994.45	$994.50