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	$40.50	3.802%	$42.0398	$42.04	$42.05	$42.00
Purchase #2	$43.90	13.627%	$49.8823	$49.88	$49.90	$49.90
Purchase #3	$234.87	8.711%	$255.3295	$255.33	$255.35	$255.30
Purchase #4	$218.51	7.262%	$234.3782	$234.38	$234.40	$234.40
Purchase #5	$152.85	12.702%	$172.265	$172.27	$172.25	$172.30
Purchase #6	$212.82	7.692%	$229.1901	$229.19	$229.20	$229.20
Purchase #7	$171.38	7.608%	$184.4186	$184.42	$184.40	$184.40
7 purchase totals =	$1,074.83		$1,167.5035	$1,167.51	$1,167.55	$1,167.50