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	$104.71	10.694%	$115.9077	$115.91	$115.90	$115.90
Purchase #2	$230.48	6.216%	$244.8066	$244.81	$244.80	$244.80
Purchase #3	$165.70	11.653%	$185.009	$185.01	$185.00	$185.00
Purchase #4	$224.45	8.186%	$242.8235	$242.82	$242.80	$242.80
Purchase #5	$46.86	12.505%	$52.7198	$52.72	$52.70	$52.70
Purchase #6	$55.40	13.571%	$62.9183	$62.92	$62.90	$62.90
Purchase #7	$66.99	6.610%	$71.418	$71.42	$71.40	$71.40
7 purchase totals =	$894.59		$975.6029	$975.61	$975.50	$975.50