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	$29.97	5.595%	$31.6468	$31.65	$31.65	$31.60
Purchase #2	$99.68	12.177%	$111.818	$111.82	$111.80	$111.80
Purchase #3	$210.96	7.579%	$226.9487	$226.95	$226.95	$226.90
Purchase #4	$95.97	13.706%	$109.1236	$109.12	$109.10	$109.10
Purchase #5	$136.38	11.459%	$152.0078	$152.01	$152.00	$152.00
Purchase #6	$12.73	11.418%	$14.1835	$14.18	$14.20	$14.20
Purchase #7	$124.73	9.105%	$136.0867	$136.09	$136.10	$136.10
7 purchase totals =	$710.42		$781.8151	$781.82	$781.80	$781.70