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	$124.32	12.753%	$140.1745	$140.17	$140.15	$140.20
Purchase #2	$129.52	11.632%	$144.5858	$144.59	$144.60	$144.60
Purchase #3	$239.44	3.355%	$247.4732	$247.47	$247.45	$247.50
Purchase #4	$89.47	13.262%	$101.3355	$101.34	$101.35	$101.30
Purchase #5	$175.39	9.436%	$191.9398	$191.94	$191.95	$191.90
Purchase #6	$78.67	6.547%	$83.8205	$83.82	$83.80	$83.80
Purchase #7	$239.29	12.718%	$269.7229	$269.72	$269.70	$269.70
7 purchase totals =	$1,076.10		$1,179.0522	$1,179.05	$1,179.00	$1,179.00