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	$139.89	13.236%	$158.4058	$158.41	$158.40	$158.40
Purchase #2	$106.58	5.810%	$112.7723	$112.77	$112.75	$112.80
Purchase #3	$144.54	5.598%	$152.6313	$152.63	$152.65	$152.60
Purchase #4	$241.33	7.684%	$259.8738	$259.87	$259.85	$259.90
Purchase #5	$162.32	7.812%	$175.0004	$175.00	$175.00	$175.00
Purchase #6	$188.88	12.169%	$211.8648	$211.86	$211.85	$211.90
Purchase #7	$31.79	10.501%	$35.1283	$35.13	$35.15	$35.10
7 purchase totals =	$1,015.33		$1,105.6767	$1,105.67	$1,105.65	$1,105.70