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	$78.66	12.363%	$88.3847	$88.38	$88.40	$88.40
Purchase #2	$55.83	11.363%	$62.174	$62.17	$62.15	$62.20
Purchase #3	$248.37	8.465%	$269.3945	$269.39	$269.40	$269.40
Purchase #4	$247.74	13.386%	$280.9025	$280.90	$280.90	$280.90
Purchase #5	$129.48	7.585%	$139.3011	$139.30	$139.30	$139.30
Purchase #6	$34.25	12.631%	$38.5761	$38.58	$38.60	$38.60
Purchase #7	$142.58	12.827%	$160.8687	$160.87	$160.85	$160.90
7 purchase totals =	$936.91		$1,039.6016	$1,039.59	$1,039.60	$1,039.70