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	$130.89	5.795%	$138.4751	$138.48	$138.50	$138.50
Purchase #2	$67.38	5.425%	$71.0354	$71.04	$71.05	$71.00
Purchase #3	$109.40	12.650%	$123.2391	$123.24	$123.25	$123.20
Purchase #4	$50.50	6.255%	$53.6588	$53.66	$53.65	$53.70
Purchase #5	$159.96	11.305%	$178.0435	$178.04	$178.05	$178.00
Purchase #6	$50.37	4.466%	$52.6195	$52.62	$52.60	$52.60
Purchase #7	$88.84	11.286%	$98.8665	$98.87	$98.85	$98.90
7 purchase totals =	$657.34		$715.9379	$715.95	$715.95	$715.90