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	$29.68	9.862%	$32.607	$32.61	$32.60	$32.60
Purchase #2	$121.43	3.847%	$126.1014	$126.10	$126.10	$126.10
Purchase #3	$135.40	4.562%	$141.5769	$141.58	$141.60	$141.60
Purchase #4	$164.39	12.636%	$185.1623	$185.16	$185.15	$185.20
Purchase #5	$71.53	6.530%	$76.2009	$76.20	$76.20	$76.20
Purchase #6	$173.73	13.289%	$196.817	$196.82	$196.80	$196.80
Purchase #7	$193.73	8.372%	$209.9491	$209.95	$209.95	$209.90
7 purchase totals =	$889.89		$968.4146	$968.42	$968.40	$968.40