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	$61.57	5.753%	$65.1121	$65.11	$65.10	$65.10
Purchase #2	$38.35	8.195%	$41.4928	$41.49	$41.50	$41.50
Purchase #3	$72.54	10.623%	$80.2459	$80.25	$80.25	$80.20
Purchase #4	$238.82	4.578%	$249.7532	$249.75	$249.75	$249.80
Purchase #5	$196.85	10.162%	$216.8539	$216.85	$216.85	$216.90
Purchase #6	$173.44	5.684%	$183.2983	$183.30	$183.30	$183.30
Purchase #7	$38.25	5.590%	$40.3882	$40.39	$40.40	$40.40
7 purchase totals =	$819.82		$877.1444	$877.14	$877.15	$877.20