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	$47.54	10.674%	$52.6144	$52.61	$52.60	$52.60
Purchase #2	$34.50	4.709%	$36.1246	$36.12	$36.10	$36.10
Purchase #3	$250.52	4.153%	$260.9241	$260.92	$260.90	$260.90
Purchase #4	$172.25	7.729%	$185.5632	$185.56	$185.55	$185.60
Purchase #5	$99.28	12.547%	$111.7367	$111.74	$111.75	$111.70
Purchase #6	$106.51	7.224%	$114.2043	$114.20	$114.20	$114.20
Purchase #7	$147.64	12.374%	$165.909	$165.91	$165.90	$165.90
7 purchase totals =	$858.24		$927.0763	$927.06	$927.00	$927.00