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	$146.54	12.322%	$164.5967	$164.60	$164.60	$164.60
Purchase #2	$184.88	4.615%	$193.4122	$193.41	$193.40	$193.40
Purchase #3	$113.49	12.545%	$127.7273	$127.73	$127.75	$127.70
Purchase #4	$73.61	12.114%	$82.5271	$82.53	$82.55	$82.50
Purchase #5	$168.37	3.415%	$174.1198	$174.12	$174.10	$174.10
Purchase #6	$61.48	7.871%	$66.3191	$66.32	$66.30	$66.30
Purchase #7	$25.42	10.167%	$28.0045	$28.00	$28.00	$28.00
7 purchase totals =	$773.79		$836.7067	$836.71	$836.70	$836.60