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	$9.84	5.497%	$10.3809	$10.38	$10.40	$10.40
Purchase #2	$190.48	13.113%	$215.4576	$215.46	$215.45	$215.50
Purchase #3	$99.41	12.177%	$111.5152	$111.52	$111.50	$111.50
Purchase #4	$235.56	11.187%	$261.9121	$261.91	$261.90	$261.90
Purchase #5	$79.38	4.785%	$83.1783	$83.18	$83.20	$83.20
Purchase #6	$57.90	7.363%	$62.1632	$62.16	$62.15	$62.20
Purchase #7	$20.56	11.205%	$22.8637	$22.86	$22.85	$22.90
7 purchase totals =	$693.13		$767.4710	$767.47	$767.45	$767.60