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	$89.71	11.360%	$99.9011	$99.90	$99.90	$99.90
Purchase #2	$53.91	11.621%	$60.1749	$60.17	$60.15	$60.20
Purchase #3	$136.92	4.360%	$142.8897	$142.89	$142.90	$142.90
Purchase #4	$62.71	10.861%	$69.5209	$69.52	$69.50	$69.50
Purchase #5	$226.84	11.333%	$252.5478	$252.55	$252.55	$252.50
Purchase #6	$40.98	6.102%	$43.4806	$43.48	$43.50	$43.50
Purchase #7	$64.32	5.570%	$67.9026	$67.90	$67.90	$67.90
7 purchase totals =	$675.39		$736.4176	$736.41	$736.40	$736.40