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	$43.53	11.431%	$48.5059	$48.51	$48.50	$48.50
Purchase #2	$77.30	11.714%	$86.3549	$86.35	$86.35	$86.40
Purchase #3	$241.76	11.789%	$270.2611	$270.26	$270.25	$270.30
Purchase #4	$140.77	12.797%	$158.7843	$158.78	$158.80	$158.80
Purchase #5	$113.38	9.286%	$123.9085	$123.91	$123.90	$123.90
Purchase #6	$6.81	6.541%	$7.2554	$7.26	$7.25	$7.30
Purchase #7	$128.61	5.299%	$135.425	$135.43	$135.45	$135.40
7 purchase totals =	$752.16		$830.4951	$830.50	$830.50	$830.60