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	$129.49	5.706%	$136.8787	$136.88	$136.90	$136.90
Purchase #2	$146.76	13.498%	$166.5697	$166.57	$166.55	$166.60
Purchase #3	$235.73	6.106%	$250.1237	$250.12	$250.10	$250.10
Purchase #4	$70.72	13.235%	$80.0798	$80.08	$80.10	$80.10
Purchase #5	$227.51	13.582%	$258.4104	$258.41	$258.40	$258.40
Purchase #6	$139.29	4.655%	$145.7739	$145.77	$145.75	$145.80
Purchase #7	$111.65	6.183%	$118.5533	$118.55	$118.55	$118.60
7 purchase totals =	$1,061.15		$1,156.3895	$1,156.38	$1,156.35	$1,156.50