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	$205.91	6.599%	$219.498	$219.50	$219.50	$219.50
Purchase #2	$107.78	10.263%	$118.8415	$118.84	$118.85	$118.80
Purchase #3	$50.79	10.223%	$55.9823	$55.98	$56.00	$56.00
Purchase #4	$145.39	3.632%	$150.6706	$150.67	$150.65	$150.70
Purchase #5	$135.94	12.507%	$152.942	$152.94	$152.95	$152.90
Purchase #6	$159.43	12.763%	$179.7781	$179.78	$179.80	$179.80
Purchase #7	$52.36	13.490%	$59.4234	$59.42	$59.40	$59.40
7 purchase totals =	$857.60		$937.1359	$937.13	$937.15	$937.10