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	$74.78	9.512%	$81.8931	$81.89	$81.90	$81.90
Purchase #2	$206.43	7.401%	$221.7079	$221.71	$221.70	$221.70
Purchase #3	$44.74	13.789%	$50.9092	$50.91	$50.90	$50.90
Purchase #4	$168.75	13.209%	$191.0402	$191.04	$191.05	$191.00
Purchase #5	$52.45	3.143%	$54.0985	$54.10	$54.10	$54.10
Purchase #6	$86.25	4.749%	$90.346	$90.35	$90.35	$90.30
Purchase #7	$134.53	4.180%	$140.1534	$140.15	$140.15	$140.20
7 purchase totals =	$767.93		$830.1483	$830.15	$830.15	$830.10