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	$56.61	5.488%	$59.7168	$59.72	$59.70	$59.70
Purchase #2	$107.31	4.600%	$112.2463	$112.25	$112.25	$112.20
Purchase #3	$122.57	6.603%	$130.6633	$130.66	$130.65	$130.70
Purchase #4	$241.88	8.797%	$263.1582	$263.16	$263.15	$263.20
Purchase #5	$142.29	6.186%	$151.0921	$151.09	$151.10	$151.10
Purchase #6	$174.84	8.266%	$189.2923	$189.29	$189.30	$189.30
Purchase #7	$247.34	12.772%	$278.9303	$278.93	$278.95	$278.90
7 purchase totals =	$1,092.84		$1,185.0993	$1,185.10	$1,185.10	$1,185.10