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	$96.92	3.318%	$100.1358	$100.14	$100.15	$100.10
Purchase #2	$40.94	13.685%	$46.5426	$46.54	$46.55	$46.50
Purchase #3	$8.27	4.871%	$8.6728	$8.67	$8.65	$8.70
Purchase #4	$30.50	7.602%	$32.8186	$32.82	$32.80	$32.80
Purchase #5	$151.64	6.483%	$161.4708	$161.47	$161.45	$161.50
Purchase #6	$27.83	8.200%	$30.1121	$30.11	$30.10	$30.10
Purchase #7	$118.90	10.418%	$131.287	$131.29	$131.30	$131.30
7 purchase totals =	$475.00		$511.0397	$511.04	$511.00	$511.00