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	$140.51	8.404%	$152.3185	$152.32	$152.30	$152.30
Purchase #2	$228.69	9.385%	$250.1526	$250.15	$250.15	$250.20
Purchase #3	$52.73	5.518%	$55.6396	$55.64	$55.65	$55.60
Purchase #4	$138.32	8.620%	$150.2432	$150.24	$150.25	$150.20
Purchase #5	$67.78	12.845%	$76.4863	$76.49	$76.50	$76.50
Purchase #6	$37.30	10.308%	$41.1449	$41.14	$41.15	$41.10
Purchase #7	$74.44	9.738%	$81.689	$81.69	$81.70	$81.70
7 purchase totals =	$739.77		$807.6741	$807.67	$807.70	$807.60