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	$89.30	11.682%	$99.732	$99.73	$99.75	$99.70
Purchase #2	$208.88	10.630%	$231.0839	$231.08	$231.10	$231.10
Purchase #3	$148.55	13.207%	$168.169	$168.17	$168.15	$168.20
Purchase #4	$67.80	9.299%	$74.1047	$74.10	$74.10	$74.10
Purchase #5	$224.32	10.337%	$247.508	$247.51	$247.50	$247.50
Purchase #6	$74.67	11.752%	$83.4452	$83.45	$83.45	$83.40
Purchase #7	$73.89	4.391%	$77.1345	$77.13	$77.15	$77.10
7 purchase totals =	$887.41		$981.1773	$981.17	$981.20	$981.10