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	$116.85	12.333%	$131.2611	$131.26	$131.25	$131.30
Purchase #2	$174.30	6.292%	$185.267	$185.27	$185.25	$185.30
Purchase #3	$185.62	10.396%	$204.9171	$204.92	$204.90	$204.90
Purchase #4	$184.43	8.581%	$200.2559	$200.26	$200.25	$200.30
Purchase #5	$70.48	5.437%	$74.312	$74.31	$74.30	$74.30
Purchase #6	$40.49	6.827%	$43.2543	$43.25	$43.25	$43.30
Purchase #7	$135.26	6.106%	$143.519	$143.52	$143.50	$143.50
7 purchase totals =	$907.43		$982.7864	$982.79	$982.70	$982.90