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	$51.25	3.261%	$52.9213	$52.92	$52.90	$52.90
Purchase #2	$148.51	7.371%	$159.4567	$159.46	$159.45	$159.50
Purchase #3	$30.57	6.234%	$32.4757	$32.48	$32.50	$32.50
Purchase #4	$246.40	8.477%	$267.2873	$267.29	$267.30	$267.30
Purchase #5	$84.66	7.606%	$91.0992	$91.10	$91.10	$91.10
Purchase #6	$136.69	4.409%	$142.7167	$142.72	$142.70	$142.70
Purchase #7	$141.75	8.510%	$153.8129	$153.81	$153.80	$153.80
7 purchase totals =	$839.83		$899.7698	$899.78	$899.75	$899.80