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	$17.52	3.872%	$18.1984	$18.20	$18.20	$18.20
Purchase #2	$43.57	6.467%	$46.3877	$46.39	$46.40	$46.40
Purchase #3	$118.84	4.732%	$124.4635	$124.46	$124.45	$124.50
Purchase #4	$19.65	4.828%	$20.5987	$20.60	$20.60	$20.60
Purchase #5	$42.89	3.235%	$44.2775	$44.28	$44.30	$44.30
Purchase #6	$82.41	10.768%	$91.2839	$91.28	$91.30	$91.30
Purchase #7	$50.73	3.766%	$52.6405	$52.64	$52.65	$52.60
7 purchase totals =	$375.61		$397.8502	$397.85	$397.90	$397.90