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	$67.99	12.818%	$76.705	$76.71	$76.70	$76.70
Purchase #2	$226.37	12.373%	$254.3788	$254.38	$254.40	$254.40
Purchase #3	$223.60	12.320%	$251.1475	$251.15	$251.15	$251.10
Purchase #4	$133.82	4.444%	$139.767	$139.77	$139.75	$139.80
Purchase #5	$63.32	3.467%	$65.5153	$65.52	$65.50	$65.50
Purchase #6	$37.79	4.716%	$39.5722	$39.57	$39.55	$39.60
Purchase #7	$83.31	9.734%	$91.4194	$91.42	$91.40	$91.40
7 purchase totals =	$836.20		$918.5052	$918.52	$918.45	$918.50