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	$97.32	3.579%	$100.8031	$100.80	$100.80	$100.80
Purchase #2	$111.64	11.731%	$124.7365	$124.74	$124.75	$124.70
Purchase #3	$208.59	6.233%	$221.5914	$221.59	$221.60	$221.60
Purchase #4	$155.74	9.114%	$169.9341	$169.93	$169.95	$169.90
Purchase #5	$19.93	3.399%	$20.6074	$20.61	$20.60	$20.60
Purchase #6	$228.90	3.300%	$236.4537	$236.45	$236.45	$236.50
Purchase #7	$98.30	11.629%	$109.7313	$109.73	$109.75	$109.70
7 purchase totals =	$920.42		$983.8575	$983.85	$983.90	$983.80