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	$115.35	12.566%	$129.8449	$129.84	$129.85	$129.80
Purchase #2	$34.82	13.377%	$39.4779	$39.48	$39.50	$39.50
Purchase #3	$240.39	3.369%	$248.4887	$248.49	$248.50	$248.50
Purchase #4	$88.84	11.307%	$98.8851	$98.89	$98.90	$98.90
Purchase #5	$44.83	8.138%	$48.4783	$48.48	$48.50	$48.50
Purchase #6	$69.39	4.355%	$72.4119	$72.41	$72.40	$72.40
Purchase #7	$82.92	11.158%	$92.1722	$92.17	$92.15	$92.20
7 purchase totals =	$676.54		$729.7590	$729.76	$729.80	$729.80