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	$47.51	9.788%	$52.1603	$52.16	$52.15	$52.20
Purchase #2	$43.31	3.533%	$44.8401	$44.84	$44.85	$44.80
Purchase #3	$167.67	12.156%	$188.052	$188.05	$188.05	$188.10
Purchase #4	$168.41	13.713%	$191.5041	$191.50	$191.50	$191.50
Purchase #5	$10.27	11.549%	$11.4561	$11.46	$11.45	$11.50
Purchase #6	$76.48	5.485%	$80.6749	$80.67	$80.65	$80.70
Purchase #7	$233.35	13.677%	$265.2653	$265.27	$265.25	$265.30
7 purchase totals =	$747.00		$833.9528	$833.95	$833.90	$834.10