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	$102.46	6.866%	$109.4949	$109.49	$109.50	$109.50
Purchase #2	$73.97	6.635%	$78.8779	$78.88	$78.90	$78.90
Purchase #3	$33.84	10.212%	$37.2957	$37.30	$37.30	$37.30
Purchase #4	$175.68	7.531%	$188.9105	$188.91	$188.90	$188.90
Purchase #5	$163.76	7.746%	$176.4448	$176.44	$176.45	$176.40
Purchase #6	$22.28	13.751%	$25.3437	$25.34	$25.35	$25.30
Purchase #7	$241.56	11.512%	$269.3684	$269.37	$269.35	$269.40
7 purchase totals =	$813.55		$885.7359	$885.73	$885.75	$885.70