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	$198.94	11.480%	$221.7783	$221.78	$221.80	$221.80
Purchase #2	$137.85	9.249%	$150.5997	$150.60	$150.60	$150.60
Purchase #3	$212.53	9.671%	$233.0838	$233.08	$233.10	$233.10
Purchase #4	$76.61	12.484%	$86.174	$86.17	$86.15	$86.20
Purchase #5	$50.57	13.549%	$57.4217	$57.42	$57.40	$57.40
Purchase #6	$78.91	12.777%	$88.9923	$88.99	$89.00	$89.00
Purchase #7	$57.29	9.188%	$62.5538	$62.55	$62.55	$62.60
7 purchase totals =	$812.70		$900.6036	$900.59	$900.60	$900.70