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	$203.47	13.131%	$230.1876	$230.19	$230.20	$230.20
Purchase #2	$78.59	11.726%	$87.8055	$87.81	$87.80	$87.80
Purchase #3	$157.64	11.342%	$175.5195	$175.52	$175.50	$175.50
Purchase #4	$26.84	5.290%	$28.2598	$28.26	$28.25	$28.30
Purchase #5	$115.58	11.303%	$128.644	$128.64	$128.65	$128.60
Purchase #6	$165.57	12.291%	$185.9202	$185.92	$185.90	$185.90
Purchase #7	$72.51	13.743%	$82.475	$82.48	$82.50	$82.50
7 purchase totals =	$820.20		$918.8116	$918.82	$918.80	$918.80