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	$179.26	11.870%	$200.5382	$200.54	$200.55	$200.50
Purchase #2	$53.56	9.873%	$58.848	$58.85	$58.85	$58.80
Purchase #3	$99.43	6.157%	$105.5519	$105.55	$105.55	$105.60
Purchase #4	$139.90	10.553%	$154.6636	$154.66	$154.65	$154.70
Purchase #5	$134.58	11.711%	$150.3407	$150.34	$150.35	$150.30
Purchase #6	$5.92	3.830%	$6.1467	$6.15	$6.15	$6.10
Purchase #7	$77.42	4.639%	$81.0115	$81.01	$81.00	$81.00
7 purchase totals =	$690.07		$757.1006	$757.10	$757.10	$757.00