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	$30.65	9.843%	$33.6669	$33.67	$33.65	$33.70
Purchase #2	$151.95	10.720%	$168.239	$168.24	$168.25	$168.20
Purchase #3	$49.87	13.156%	$56.4309	$56.43	$56.45	$56.40
Purchase #4	$98.45	8.562%	$106.8793	$106.88	$106.90	$106.90
Purchase #5	$99.49	4.715%	$104.181	$104.18	$104.20	$104.20
Purchase #6	$28.67	11.146%	$31.8656	$31.87	$31.85	$31.90
Purchase #7	$91.84	9.373%	$100.4482	$100.45	$100.45	$100.40
7 purchase totals =	$550.92		$601.7109	$601.72	$601.75	$601.70