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	$234.76	8.569%	$254.8766	$254.88	$254.90	$254.90
Purchase #2	$172.42	5.742%	$182.3204	$182.32	$182.30	$182.30
Purchase #3	$231.80	12.244%	$260.1816	$260.18	$260.20	$260.20
Purchase #4	$38.82	5.306%	$40.8798	$40.88	$40.90	$40.90
Purchase #5	$196.51	10.205%	$216.5638	$216.56	$216.55	$216.60
Purchase #6	$26.65	4.125%	$27.7493	$27.75	$27.75	$27.70
Purchase #7	$124.58	3.326%	$128.7235	$128.72	$128.70	$128.70
7 purchase totals =	$1,025.54		$1,111.2950	$1,111.29	$1,111.30	$1,111.30