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	$172.89	11.582%	$192.9141	$192.91	$192.90	$192.90
Purchase #2	$92.27	3.415%	$95.421	$95.42	$95.40	$95.40
Purchase #3	$123.90	11.759%	$138.4694	$138.47	$138.45	$138.50
Purchase #4	$37.62	10.828%	$41.6935	$41.69	$41.70	$41.70
Purchase #5	$183.99	5.707%	$194.4903	$194.49	$194.50	$194.50
Purchase #6	$162.72	5.167%	$171.1277	$171.13	$171.15	$171.10
Purchase #7	$171.61	7.484%	$184.4533	$184.45	$184.45	$184.50
7 purchase totals =	$945.00		$1,018.5693	$1,018.56	$1,018.55	$1,018.60