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	$123.48	4.404%	$128.9181	$128.92	$128.90	$128.90
Purchase #2	$180.75	9.308%	$197.5742	$197.57	$197.55	$197.60
Purchase #3	$138.80	7.224%	$148.8269	$148.83	$148.85	$148.80
Purchase #4	$145.91	4.521%	$152.5066	$152.51	$152.50	$152.50
Purchase #5	$171.72	10.769%	$190.2125	$190.21	$190.20	$190.20
Purchase #6	$50.71	5.327%	$53.4113	$53.41	$53.40	$53.40
Purchase #7	$84.51	5.715%	$89.3397	$89.34	$89.35	$89.30
7 purchase totals =	$895.88		$960.7893	$960.79	$960.75	$960.70