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	$81.70	9.165%	$89.1878	$89.19	$89.20	$89.20
Purchase #2	$54.99	8.215%	$59.5074	$59.51	$59.50	$59.50
Purchase #3	$71.71	8.630%	$77.8986	$77.90	$77.90	$77.90
Purchase #4	$65.74	4.808%	$68.9008	$68.90	$68.90	$68.90
Purchase #5	$114.66	3.339%	$118.4885	$118.49	$118.50	$118.50
Purchase #6	$58.92	9.656%	$64.6093	$64.61	$64.60	$64.60
Purchase #7	$27.53	13.102%	$31.137	$31.14	$31.15	$31.10
7 purchase totals =	$475.25		$509.7294	$509.74	$509.75	$509.70