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	$76.46	7.602%	$82.2725	$82.27	$82.25	$82.30
Purchase #2	$181.63	13.301%	$205.7886	$205.79	$205.80	$205.80
Purchase #3	$242.45	12.712%	$273.2702	$273.27	$273.25	$273.30
Purchase #4	$7.92	4.833%	$8.3028	$8.30	$8.30	$8.30
Purchase #5	$55.45	9.757%	$60.8603	$60.86	$60.85	$60.90
Purchase #6	$78.92	12.251%	$88.5885	$88.59	$88.60	$88.60
Purchase #7	$71.78	10.602%	$79.3901	$79.39	$79.40	$79.40
7 purchase totals =	$714.61		$798.4730	$798.47	$798.45	$798.60