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	$134.53	8.199%	$145.5601	$145.56	$145.55	$145.60
Purchase #2	$219.78	8.460%	$238.3734	$238.37	$238.35	$238.40
Purchase #3	$243.71	10.624%	$269.6018	$269.60	$269.60	$269.60
Purchase #4	$100.91	4.124%	$105.0715	$105.07	$105.05	$105.10
Purchase #5	$47.91	4.612%	$50.1196	$50.12	$50.10	$50.10
Purchase #6	$95.96	13.561%	$108.9731	$108.97	$108.95	$109.00
Purchase #7	$146.88	10.548%	$162.3729	$162.37	$162.35	$162.40
7 purchase totals =	$989.68		$1,080.0724	$1,080.06	$1,079.95	$1,080.20