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	$81.74	9.470%	$89.4808	$89.48	$89.50	$89.50
Purchase #2	$68.58	4.222%	$71.4754	$71.48	$71.50	$71.50
Purchase #3	$141.74	12.862%	$159.9706	$159.97	$159.95	$160.00
Purchase #4	$69.91	7.208%	$74.9491	$74.95	$74.95	$74.90
Purchase #5	$134.77	3.152%	$139.018	$139.02	$139.00	$139.00
Purchase #6	$99.67	6.170%	$105.8196	$105.82	$105.80	$105.80
Purchase #7	$33.40	10.375%	$36.8653	$36.87	$36.85	$36.90
7 purchase totals =	$629.81		$677.5788	$677.59	$677.55	$677.60