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	$237.89	11.143%	$264.3981	$264.40	$264.40	$264.40
Purchase #2	$76.54	7.664%	$82.406	$82.41	$82.40	$82.40
Purchase #3	$64.78	4.227%	$67.5183	$67.52	$67.50	$67.50
Purchase #4	$63.99	3.773%	$66.4043	$66.40	$66.40	$66.40
Purchase #5	$25.63	7.650%	$27.5907	$27.59	$27.60	$27.60
Purchase #6	$80.30	11.674%	$89.6742	$89.67	$89.65	$89.70
Purchase #7	$175.73	8.200%	$190.1399	$190.14	$190.15	$190.10
7 purchase totals =	$724.86		$788.1315	$788.13	$788.10	$788.10