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	$60.28	9.631%	$66.0856	$66.09	$66.10	$66.10
Purchase #2	$182.94	6.458%	$194.7543	$194.75	$194.75	$194.80
Purchase #3	$27.96	11.405%	$31.1488	$31.15	$31.15	$31.10
Purchase #4	$92.94	12.531%	$104.5863	$104.59	$104.60	$104.60
Purchase #5	$179.63	7.395%	$192.9136	$192.91	$192.90	$192.90
Purchase #6	$148.90	9.393%	$162.8862	$162.89	$162.90	$162.90
Purchase #7	$235.55	12.297%	$264.5156	$264.52	$264.50	$264.50
7 purchase totals =	$928.20		$1,016.8904	$1,016.90	$1,016.90	$1,016.90