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	$50.27	4.330%	$52.4467	$52.45	$52.45	$52.40
Purchase #2	$136.35	5.296%	$143.5711	$143.57	$143.55	$143.60
Purchase #3	$47.78	7.485%	$51.3563	$51.36	$51.35	$51.40
Purchase #4	$25.62	12.757%	$28.8883	$28.89	$28.90	$28.90
Purchase #5	$105.49	3.448%	$109.1273	$109.13	$109.15	$109.10
Purchase #6	$41.33	12.141%	$46.3479	$46.35	$46.35	$46.30
Purchase #7	$209.93	5.543%	$221.5664	$221.57	$221.55	$221.60
7 purchase totals =	$616.77		$653.3040	$653.32	$653.30	$653.30