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	$60.36	10.502%	$66.699	$66.70	$66.70	$66.70
Purchase #2	$71.32	10.398%	$78.7359	$78.74	$78.75	$78.70
Purchase #3	$26.51	7.377%	$28.4656	$28.47	$28.45	$28.50
Purchase #4	$126.86	11.821%	$141.8561	$141.86	$141.85	$141.90
Purchase #5	$57.51	9.408%	$62.9205	$62.92	$62.90	$62.90
Purchase #6	$218.53	8.745%	$237.6404	$237.64	$237.65	$237.60
Purchase #7	$63.50	4.686%	$66.4756	$66.48	$66.50	$66.50
7 purchase totals =	$624.59		$682.7931	$682.81	$682.80	$682.80