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	$116.83	10.323%	$128.8904	$128.89	$128.90	$128.90
Purchase #2	$53.60	7.629%	$57.6891	$57.69	$57.70	$57.70
Purchase #3	$47.80	5.510%	$50.4338	$50.43	$50.45	$50.40
Purchase #4	$202.68	13.293%	$229.6223	$229.62	$229.60	$229.60
Purchase #5	$32.43	6.871%	$34.6583	$34.66	$34.65	$34.70
Purchase #6	$83.60	7.107%	$89.5415	$89.54	$89.55	$89.50
Purchase #7	$104.78	3.601%	$108.5531	$108.55	$108.55	$108.60
7 purchase totals =	$641.72		$699.3885	$699.38	$699.40	$699.40