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	$89.96	10.374%	$99.2925	$99.29	$99.30	$99.30
Purchase #2	$73.46	7.134%	$78.7006	$78.70	$78.70	$78.70
Purchase #3	$139.40	6.541%	$148.5182	$148.52	$148.50	$148.50
Purchase #4	$16.36	11.847%	$18.2982	$18.30	$18.30	$18.30
Purchase #5	$146.73	6.379%	$156.0899	$156.09	$156.10	$156.10
Purchase #6	$41.33	13.281%	$46.819	$46.82	$46.80	$46.80
Purchase #7	$64.58	8.435%	$70.0273	$70.03	$70.05	$70.00
7 purchase totals =	$571.82		$617.7457	$617.75	$617.75	$617.70