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	$48.62	4.597%	$50.8551	$50.86	$50.85	$50.90
Purchase #2	$101.66	10.641%	$112.4776	$112.48	$112.50	$112.50
Purchase #3	$154.89	4.857%	$162.413	$162.41	$162.40	$162.40
Purchase #4	$98.67	5.176%	$103.7772	$103.78	$103.80	$103.80
Purchase #5	$51.80	4.787%	$54.2797	$54.28	$54.30	$54.30
Purchase #6	$54.26	3.669%	$56.2508	$56.25	$56.25	$56.30
Purchase #7	$6.47	7.715%	$6.9692	$6.97	$6.95	$7.00
7 purchase totals =	$516.37		$547.0226	$547.03	$547.05	$547.20