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	$117.87	11.528%	$131.4581	$131.46	$131.45	$131.50
Purchase #2	$188.89	10.457%	$208.6422	$208.64	$208.65	$208.60
Purchase #3	$77.33	6.524%	$82.375	$82.38	$82.40	$82.40
Purchase #4	$29.87	7.618%	$32.1455	$32.15	$32.15	$32.10
Purchase #5	$130.45	7.154%	$139.7824	$139.78	$139.80	$139.80
Purchase #6	$91.93	13.608%	$104.4398	$104.44	$104.45	$104.40
Purchase #7	$219.95	12.726%	$247.9408	$247.94	$247.95	$247.90
7 purchase totals =	$856.29		$946.7838	$946.79	$946.85	$946.70