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	$240.82	6.123%	$255.5654	$255.57	$255.55	$255.60
Purchase #2	$151.44	8.609%	$164.4775	$164.48	$164.50	$164.50
Purchase #3	$203.83	12.454%	$229.215	$229.22	$229.20	$229.20
Purchase #4	$140.89	8.124%	$152.3359	$152.34	$152.35	$152.30
Purchase #5	$21.31	13.414%	$24.1685	$24.17	$24.15	$24.20
Purchase #6	$193.81	9.234%	$211.7064	$211.71	$211.70	$211.70
Purchase #7	$43.36	10.811%	$48.0476	$48.05	$48.05	$48.00
7 purchase totals =	$995.46		$1,085.5163	$1,085.54	$1,085.50	$1,085.50