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	$249.44	11.149%	$277.2501	$277.25	$277.25	$277.30
Purchase #2	$38.73	5.713%	$40.9426	$40.94	$40.95	$40.90
Purchase #3	$240.41	5.594%	$253.8585	$253.86	$253.85	$253.90
Purchase #4	$134.71	12.480%	$151.5218	$151.52	$151.50	$151.50
Purchase #5	$54.63	3.708%	$56.6557	$56.66	$56.65	$56.70
Purchase #6	$229.64	11.387%	$255.7891	$255.79	$255.80	$255.80
Purchase #7	$36.70	13.241%	$41.5594	$41.56	$41.55	$41.60
7 purchase totals =	$984.26		$1,077.5772	$1,077.58	$1,077.55	$1,077.70