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	$103.67	5.324%	$109.1894	$109.19	$109.20	$109.20
Purchase #2	$95.52	4.756%	$100.0629	$100.06	$100.05	$100.10
Purchase #3	$30.33	5.834%	$32.0995	$32.10	$32.10	$32.10
Purchase #4	$93.38	7.684%	$100.5553	$100.56	$100.55	$100.60
Purchase #5	$46.76	8.298%	$50.6401	$50.64	$50.65	$50.60
Purchase #6	$44.82	6.674%	$47.8113	$47.81	$47.80	$47.80
Purchase #7	$109.32	10.617%	$120.9265	$120.93	$120.95	$120.90
7 purchase totals =	$523.80		$561.2850	$561.29	$561.30	$561.30