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	$243.41	6.181%	$258.4552	$258.46	$258.45	$258.50
Purchase #2	$206.27	3.633%	$213.7638	$213.76	$213.75	$213.80
Purchase #3	$62.60	6.422%	$66.6202	$66.62	$66.60	$66.60
Purchase #4	$155.78	10.376%	$171.9437	$171.94	$171.95	$171.90
Purchase #5	$213.27	3.428%	$220.5809	$220.58	$220.60	$220.60
Purchase #6	$73.39	6.658%	$78.2763	$78.28	$78.30	$78.30
Purchase #7	$16.83	9.775%	$18.4751	$18.48	$18.50	$18.50
7 purchase totals =	$971.55		$1,028.1152	$1,028.12	$1,028.15	$1,028.20