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	$30.84	6.625%	$32.8832	$32.88	$32.90	$32.90
Purchase #2	$224.55	11.775%	$250.9908	$250.99	$251.00	$251.00
Purchase #3	$59.51	6.261%	$63.2359	$63.24	$63.25	$63.20
Purchase #4	$38.58	13.742%	$43.8817	$43.88	$43.90	$43.90
Purchase #5	$51.80	3.826%	$53.7819	$53.78	$53.80	$53.80
Purchase #6	$75.89	12.187%	$85.1387	$85.14	$85.15	$85.10
Purchase #7	$53.60	11.290%	$59.6514	$59.65	$59.65	$59.70
7 purchase totals =	$534.77		$589.5636	$589.56	$589.65	$589.60