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	$157.36	13.678%	$178.8837	$178.88	$178.90	$178.90
Purchase #2	$89.47	3.397%	$92.5093	$92.51	$92.50	$92.50
Purchase #3	$113.34	6.866%	$121.1219	$121.12	$121.10	$121.10
Purchase #4	$238.55	8.315%	$258.3854	$258.39	$258.40	$258.40
Purchase #5	$154.77	9.768%	$169.8879	$169.89	$169.90	$169.90
Purchase #6	$221.46	10.277%	$244.2194	$244.22	$244.20	$244.20
Purchase #7	$44.39	4.102%	$46.2109	$46.21	$46.20	$46.20
7 purchase totals =	$1,019.34		$1,111.2185	$1,111.22	$1,111.20	$1,111.20