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	$68.57	3.381%	$70.8884	$70.89	$70.90	$70.90
Purchase #2	$140.87	6.561%	$150.1125	$150.11	$150.10	$150.10
Purchase #3	$155.69	10.395%	$171.874	$171.87	$171.85	$171.90
Purchase #4	$15.52	8.440%	$16.8299	$16.83	$16.85	$16.80
Purchase #5	$53.50	5.630%	$56.5121	$56.51	$56.50	$56.50
Purchase #6	$74.26	10.850%	$82.3172	$82.32	$82.30	$82.30
Purchase #7	$41.34	12.261%	$46.4087	$46.41	$46.40	$46.40
7 purchase totals =	$549.75		$594.9428	$594.94	$594.90	$594.90