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	$79.88	9.868%	$87.7626	$87.76	$87.75	$87.80
Purchase #2	$78.76	4.291%	$82.1396	$82.14	$82.15	$82.10
Purchase #3	$80.88	5.428%	$85.2702	$85.27	$85.25	$85.30
Purchase #4	$238.46	4.316%	$248.7519	$248.75	$248.75	$248.80
Purchase #5	$54.71	8.627%	$59.4298	$59.43	$59.45	$59.40
Purchase #6	$71.30	9.717%	$78.2282	$78.23	$78.25	$78.20
Purchase #7	$175.75	7.547%	$189.0139	$189.01	$189.00	$189.00
7 purchase totals =	$779.74		$830.5962	$830.59	$830.60	$830.60