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	$109.89	12.384%	$123.4988	$123.50	$123.50	$123.50
Purchase #2	$231.68	9.777%	$254.3314	$254.33	$254.35	$254.30
Purchase #3	$185.31	9.864%	$203.589	$203.59	$203.60	$203.60
Purchase #4	$133.47	13.330%	$151.2616	$151.26	$151.25	$151.30
Purchase #5	$215.30	7.670%	$231.8135	$231.81	$231.80	$231.80
Purchase #6	$191.26	4.428%	$199.729	$199.73	$199.75	$199.70
Purchase #7	$179.40	6.373%	$190.8332	$190.83	$190.85	$190.80
7 purchase totals =	$1,246.31		$1,355.0565	$1,355.05	$1,355.10	$1,355.00