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	$152.26	13.573%	$172.9262	$172.93	$172.95	$172.90
Purchase #2	$83.48	6.393%	$88.8169	$88.82	$88.80	$88.80
Purchase #3	$231.34	6.820%	$247.1174	$247.12	$247.10	$247.10
Purchase #4	$133.65	9.452%	$146.2826	$146.28	$146.30	$146.30
Purchase #5	$231.96	12.709%	$261.4398	$261.44	$261.45	$261.40
Purchase #6	$81.72	13.155%	$92.4703	$92.47	$92.45	$92.50
Purchase #7	$51.76	3.416%	$53.5281	$53.53	$53.55	$53.50
7 purchase totals =	$966.17		$1,062.5813	$1,062.59	$1,062.60	$1,062.50