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	$26.73	9.558%	$29.2849	$29.28	$29.30	$29.30
Purchase #2	$98.27	5.661%	$103.8331	$103.83	$103.85	$103.80
Purchase #3	$105.43	6.475%	$112.2566	$112.26	$112.25	$112.30
Purchase #4	$130.53	13.317%	$147.9127	$147.91	$147.90	$147.90
Purchase #5	$85.97	5.697%	$90.8677	$90.87	$90.85	$90.90
Purchase #6	$177.51	8.456%	$192.5202	$192.52	$192.50	$192.50
Purchase #7	$243.33	7.429%	$261.407	$261.41	$261.40	$261.40
7 purchase totals =	$867.77		$938.0822	$938.08	$938.05	$938.10