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	$65.85	9.484%	$72.0952	$72.10	$72.10	$72.10
Purchase #2	$99.28	5.479%	$104.7196	$104.72	$104.70	$104.70
Purchase #3	$121.35	10.809%	$134.4667	$134.47	$134.45	$134.50
Purchase #4	$165.76	11.654%	$185.0777	$185.08	$185.10	$185.10
Purchase #5	$243.89	6.214%	$259.0453	$259.05	$259.05	$259.00
Purchase #6	$127.72	6.441%	$135.9464	$135.95	$135.95	$135.90
Purchase #7	$138.36	7.340%	$148.5156	$148.52	$148.50	$148.50
7 purchase totals =	$962.21		$1,039.8665	$1,039.89	$1,039.85	$1,039.80