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	$7.43	8.797%	$8.0836	$8.08	$8.10	$8.10
Purchase #2	$89.89	12.773%	$101.3716	$101.37	$101.35	$101.40
Purchase #3	$25.57	11.647%	$28.5481	$28.55	$28.55	$28.50
Purchase #4	$169.39	9.776%	$185.9496	$185.95	$185.95	$185.90
Purchase #5	$227.33	9.813%	$249.6379	$249.64	$249.65	$249.60
Purchase #6	$139.51	10.590%	$154.2841	$154.28	$154.30	$154.30
Purchase #7	$248.27	9.719%	$272.3994	$272.40	$272.40	$272.40
7 purchase totals =	$907.39		$1,000.2743	$1,000.27	$1,000.30	$1,000.20