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	$41.68	12.494%	$46.8875	$46.89	$46.90	$46.90
Purchase #2	$11.40	11.687%	$12.7323	$12.73	$12.75	$12.70
Purchase #3	$165.73	8.526%	$179.8601	$179.86	$179.85	$179.90
Purchase #4	$42.39	7.776%	$45.6862	$45.69	$45.70	$45.70
Purchase #5	$219.94	12.683%	$247.835	$247.84	$247.85	$247.80
Purchase #6	$32.53	10.228%	$35.8572	$35.86	$35.85	$35.90
Purchase #7	$87.48	5.235%	$92.0596	$92.06	$92.05	$92.10
7 purchase totals =	$601.15		$660.9179	$660.93	$660.95	$661.00