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	$150.89	13.528%	$171.3024	$171.30	$171.30	$171.30
Purchase #2	$229.66	5.519%	$242.3349	$242.33	$242.35	$242.30
Purchase #3	$145.39	6.198%	$154.4013	$154.40	$154.40	$154.40
Purchase #4	$171.58	5.164%	$180.4404	$180.44	$180.45	$180.40
Purchase #5	$43.49	11.360%	$48.4305	$48.43	$48.45	$48.40
Purchase #6	$60.51	12.265%	$67.9316	$67.93	$67.95	$67.90
Purchase #7	$59.40	4.717%	$62.2019	$62.20	$62.20	$62.20
7 purchase totals =	$860.92		$927.0430	$927.03	$927.10	$926.90