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	$53.54	13.704%	$60.8771	$60.88	$60.90	$60.90
Purchase #2	$143.46	11.289%	$159.6552	$159.66	$159.65	$159.70
Purchase #3	$206.91	4.288%	$215.7823	$215.78	$215.80	$215.80
Purchase #4	$73.46	5.273%	$77.3335	$77.33	$77.35	$77.30
Purchase #5	$211.43	7.593%	$227.4839	$227.48	$227.50	$227.50
Purchase #6	$228.92	8.608%	$248.6254	$248.63	$248.65	$248.60
Purchase #7	$90.76	5.140%	$95.4251	$95.43	$95.45	$95.40
7 purchase totals =	$1,008.48		$1,085.1825	$1,085.19	$1,085.30	$1,085.20