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	$82.46	8.352%	$89.3471	$89.35	$89.35	$89.30
Purchase #2	$239.93	12.553%	$270.0484	$270.05	$270.05	$270.00
Purchase #3	$39.58	13.872%	$45.0705	$45.07	$45.05	$45.10
Purchase #4	$111.72	8.262%	$120.9503	$120.95	$120.95	$121.00
Purchase #5	$34.65	13.836%	$39.4442	$39.44	$39.45	$39.40
Purchase #6	$99.66	11.615%	$111.2355	$111.24	$111.25	$111.20
Purchase #7	$183.34	9.228%	$200.2586	$200.26	$200.25	$200.30
7 purchase totals =	$791.34		$876.3546	$876.36	$876.35	$876.30