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	$183.73	9.136%	$200.5156	$200.52	$200.50	$200.50
Purchase #2	$246.47	13.756%	$280.3744	$280.37	$280.35	$280.40
Purchase #3	$178.38	8.840%	$194.1488	$194.15	$194.15	$194.10
Purchase #4	$244.48	13.155%	$276.6413	$276.64	$276.65	$276.60
Purchase #5	$115.60	13.830%	$131.5875	$131.59	$131.60	$131.60
Purchase #6	$68.54	12.494%	$77.1034	$77.10	$77.10	$77.10
Purchase #7	$23.92	5.423%	$25.2172	$25.22	$25.20	$25.20
7 purchase totals =	$1,061.12		$1,185.5882	$1,185.59	$1,185.55	$1,185.50