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	$58.77	5.720%	$62.1316	$62.13	$62.15	$62.10
Purchase #2	$56.44	5.756%	$59.6887	$59.69	$59.70	$59.70
Purchase #3	$182.82	9.167%	$199.5791	$199.58	$199.60	$199.60
Purchase #4	$11.84	12.378%	$13.3056	$13.31	$13.30	$13.30
Purchase #5	$148.34	7.126%	$158.9107	$158.91	$158.90	$158.90
Purchase #6	$216.37	12.472%	$243.3557	$243.36	$243.35	$243.40
Purchase #7	$98.78	12.603%	$111.2292	$111.23	$111.25	$111.20
7 purchase totals =	$773.36		$848.2006	$848.21	$848.25	$848.20