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	$21.44	12.683%	$24.1592	$24.16	$24.15	$24.20
Purchase #2	$236.90	11.387%	$263.8758	$263.88	$263.90	$263.90
Purchase #3	$48.68	13.685%	$55.3419	$55.34	$55.35	$55.30
Purchase #4	$218.59	6.647%	$233.1197	$233.12	$233.10	$233.10
Purchase #5	$179.91	5.782%	$190.3124	$190.31	$190.30	$190.30
Purchase #6	$133.71	8.694%	$145.3347	$145.33	$145.35	$145.30
Purchase #7	$90.85	9.206%	$99.2137	$99.21	$99.20	$99.20
7 purchase totals =	$930.08		$1,011.3574	$1,011.35	$1,011.35	$1,011.30