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	$99.82	4.403%	$104.2151	$104.22	$104.20	$104.20
Purchase #2	$131.28	7.127%	$140.6363	$140.64	$140.65	$140.60
Purchase #3	$126.54	7.227%	$135.685	$135.69	$135.70	$135.70
Purchase #4	$59.88	9.317%	$65.459	$65.46	$65.45	$65.50
Purchase #5	$27.79	6.555%	$29.6116	$29.61	$29.60	$29.60
Purchase #6	$56.73	4.114%	$59.0639	$59.06	$59.05	$59.10
Purchase #7	$42.92	12.310%	$48.2035	$48.20	$48.20	$48.20
7 purchase totals =	$544.96		$582.8744	$582.88	$582.85	$582.90