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	$92.54	10.762%	$102.4992	$102.50	$102.50	$102.50
Purchase #2	$56.82	7.725%	$61.2093	$61.21	$61.20	$61.20
Purchase #3	$45.77	4.548%	$47.8516	$47.85	$47.85	$47.90
Purchase #4	$206.63	4.822%	$216.5937	$216.59	$216.60	$216.60
Purchase #5	$29.44	6.248%	$31.2794	$31.28	$31.30	$31.30
Purchase #6	$47.55	12.498%	$53.4928	$53.49	$53.50	$53.50
Purchase #7	$202.75	12.618%	$228.333	$228.33	$228.35	$228.30
7 purchase totals =	$681.50		$741.2590	$741.25	$741.30	$741.30