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	$46.34	11.826%	$51.8202	$51.82	$51.80	$51.80
Purchase #2	$189.88	5.734%	$200.7677	$200.77	$200.75	$200.80
Purchase #3	$151.44	8.497%	$164.3079	$164.31	$164.30	$164.30
Purchase #4	$230.45	12.574%	$259.4268	$259.43	$259.45	$259.40
Purchase #5	$140.84	3.195%	$145.3398	$145.34	$145.35	$145.30
Purchase #6	$196.51	6.559%	$209.3991	$209.40	$209.40	$209.40
Purchase #7	$177.94	7.859%	$191.9243	$191.92	$191.90	$191.90
7 purchase totals =	$1,133.40		$1,222.9858	$1,222.99	$1,222.95	$1,222.90