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	$91.62	8.406%	$99.3216	$99.32	$99.30	$99.30
Purchase #2	$207.98	3.805%	$215.8936	$215.89	$215.90	$215.90
Purchase #3	$129.38	12.667%	$145.7686	$145.77	$145.75	$145.80
Purchase #4	$48.83	10.569%	$53.9908	$53.99	$54.00	$54.00
Purchase #5	$35.67	10.192%	$39.3055	$39.31	$39.30	$39.30
Purchase #6	$102.32	3.203%	$105.5973	$105.60	$105.60	$105.60
Purchase #7	$42.66	7.614%	$45.9081	$45.91	$45.90	$45.90
7 purchase totals =	$658.46		$705.7855	$705.79	$705.75	$705.80