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	$168.79	3.436%	$174.5896	$174.59	$174.60	$174.60
Purchase #2	$45.95	12.870%	$51.8638	$51.86	$51.85	$51.90
Purchase #3	$144.55	11.294%	$160.8755	$160.88	$160.90	$160.90
Purchase #4	$133.85	13.157%	$151.4606	$151.46	$151.45	$151.50
Purchase #5	$141.31	4.854%	$148.1692	$148.17	$148.15	$148.20
Purchase #6	$73.63	5.734%	$77.8519	$77.85	$77.85	$77.90
Purchase #7	$153.84	5.461%	$162.2412	$162.24	$162.25	$162.20
7 purchase totals =	$861.92		$927.0518	$927.05	$927.05	$927.20