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	$8.43	12.797%	$9.5088	$9.51	$9.50	$9.50
Purchase #2	$48.86	13.540%	$55.4756	$55.48	$55.50	$55.50
Purchase #3	$122.89	3.468%	$127.1518	$127.15	$127.15	$127.20
Purchase #4	$237.44	11.329%	$264.3396	$264.34	$264.35	$264.30
Purchase #5	$120.49	5.856%	$127.5459	$127.55	$127.55	$127.50
Purchase #6	$213.53	11.690%	$238.4917	$238.49	$238.50	$238.50
Purchase #7	$211.68	10.744%	$234.4229	$234.42	$234.40	$234.40
7 purchase totals =	$963.32		$1,056.9363	$1,056.94	$1,056.95	$1,056.90