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	$80.80	4.138%	$84.1435	$84.14	$84.15	$84.10
Purchase #2	$13.98	3.422%	$14.4584	$14.46	$14.45	$14.50
Purchase #3	$223.86	13.782%	$254.7124	$254.71	$254.70	$254.70
Purchase #4	$18.94	10.792%	$20.984	$20.98	$21.00	$21.00
Purchase #5	$112.57	12.874%	$127.0623	$127.06	$127.05	$127.10
Purchase #6	$27.33	4.460%	$28.5489	$28.55	$28.55	$28.50
Purchase #7	$25.28	10.805%	$28.0115	$28.01	$28.00	$28.00
7 purchase totals =	$502.76		$557.9210	$557.91	$557.90	$557.90