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	$225.83	12.816%	$254.7724	$254.77	$254.75	$254.80
Purchase #2	$239.93	3.328%	$247.9149	$247.91	$247.90	$247.90
Purchase #3	$185.54	3.405%	$191.8576	$191.86	$191.85	$191.90
Purchase #4	$183.65	13.576%	$208.5823	$208.58	$208.60	$208.60
Purchase #5	$102.56	6.587%	$109.3156	$109.32	$109.30	$109.30
Purchase #6	$229.76	13.812%	$261.4945	$261.49	$261.50	$261.50
Purchase #7	$129.90	12.592%	$146.257	$146.26	$146.25	$146.30
7 purchase totals =	$1,297.17		$1,420.1943	$1,420.19	$1,420.15	$1,420.30