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	$180.80	4.290%	$188.5563	$188.56	$188.55	$188.60
Purchase #2	$31.88	8.662%	$34.6414	$34.64	$34.65	$34.60
Purchase #3	$95.33	12.149%	$106.9116	$106.91	$106.90	$106.90
Purchase #4	$11.83	11.699%	$13.214	$13.21	$13.20	$13.20
Purchase #5	$37.38	11.776%	$41.7819	$41.78	$41.80	$41.80
Purchase #6	$53.80	10.391%	$59.3904	$59.39	$59.40	$59.40
Purchase #7	$131.80	5.383%	$138.8948	$138.89	$138.90	$138.90
7 purchase totals =	$542.82		$583.3904	$583.38	$583.40	$583.40