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	$78.74	13.372%	$89.2691	$89.27	$89.25	$89.30
Purchase #2	$124.56	5.537%	$131.4569	$131.46	$131.45	$131.50
Purchase #3	$132.58	7.748%	$142.8523	$142.85	$142.85	$142.90
Purchase #4	$106.93	6.211%	$113.5714	$113.57	$113.55	$113.60
Purchase #5	$176.73	12.803%	$199.3567	$199.36	$199.35	$199.40
Purchase #6	$55.96	7.453%	$60.1307	$60.13	$60.15	$60.10
Purchase #7	$184.47	4.311%	$192.4225	$192.42	$192.40	$192.40
7 purchase totals =	$859.97		$929.0596	$929.06	$929.00	$929.20