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	$37.83	5.262%	$39.8206	$39.82	$39.80	$39.80
Purchase #2	$63.73	7.122%	$68.2689	$68.27	$68.25	$68.30
Purchase #3	$239.39	11.482%	$266.8768	$266.88	$266.90	$266.90
Purchase #4	$145.25	6.190%	$154.241	$154.24	$154.25	$154.20
Purchase #5	$120.58	6.577%	$128.5105	$128.51	$128.50	$128.50
Purchase #6	$250.73	9.749%	$275.1737	$275.17	$275.15	$275.20
Purchase #7	$71.77	9.736%	$78.7575	$78.76	$78.75	$78.80
7 purchase totals =	$929.28		$1,011.6490	$1,011.65	$1,011.60	$1,011.70