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	$69.82	4.553%	$72.9989	$73.00	$73.00	$73.00
Purchase #2	$52.64	6.262%	$55.9363	$55.94	$55.95	$55.90
Purchase #3	$219.72	10.637%	$243.0916	$243.09	$243.10	$243.10
Purchase #4	$90.33	13.377%	$102.4134	$102.41	$102.40	$102.40
Purchase #5	$129.66	9.147%	$141.52	$141.52	$141.50	$141.50
Purchase #6	$31.28	4.814%	$32.7858	$32.79	$32.80	$32.80
Purchase #7	$11.47	9.611%	$12.5724	$12.57	$12.55	$12.60
7 purchase totals =	$604.92		$661.3184	$661.32	$661.30	$661.30