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	$49.79	9.468%	$54.5041	$54.50	$54.50	$54.50
Purchase #2	$133.95	8.839%	$145.7898	$145.79	$145.80	$145.80
Purchase #3	$31.30	7.340%	$33.5974	$33.60	$33.60	$33.60
Purchase #4	$128.87	8.271%	$139.5288	$139.53	$139.55	$139.50
Purchase #5	$210.47	13.364%	$238.5972	$238.60	$238.60	$238.60
Purchase #6	$85.52	13.222%	$96.8275	$96.83	$96.85	$96.80
Purchase #7	$162.37	4.874%	$170.2839	$170.28	$170.30	$170.30
7 purchase totals =	$802.27		$879.1287	$879.13	$879.20	$879.10