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	$206.88	8.596%	$224.6634	$224.66	$224.65	$224.70
Purchase #2	$92.66	7.817%	$99.9032	$99.90	$99.90	$99.90
Purchase #3	$132.73	6.679%	$141.595	$141.60	$141.60	$141.60
Purchase #4	$92.50	13.712%	$105.1836	$105.18	$105.20	$105.20
Purchase #5	$139.99	7.815%	$150.9302	$150.93	$150.95	$150.90
Purchase #6	$197.41	7.136%	$211.4972	$211.50	$211.50	$211.50
Purchase #7	$59.65	10.130%	$65.6925	$65.69	$65.70	$65.70
7 purchase totals =	$921.82		$999.4651	$999.46	$999.50	$999.50