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	$127.51	4.224%	$132.896	$132.90	$132.90	$132.90
Purchase #2	$181.48	3.670%	$188.1403	$188.14	$188.15	$188.10
Purchase #3	$59.83	9.715%	$65.6425	$65.64	$65.65	$65.60
Purchase #4	$37.73	4.174%	$39.3049	$39.30	$39.30	$39.30
Purchase #5	$210.60	6.843%	$225.0114	$225.01	$225.00	$225.00
Purchase #6	$170.53	12.139%	$191.2306	$191.23	$191.25	$191.20
Purchase #7	$184.73	8.372%	$200.1956	$200.20	$200.20	$200.20
7 purchase totals =	$972.41		$1,042.4213	$1,042.42	$1,042.45	$1,042.30