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	$100.41	9.346%	$109.7943	$109.79	$109.80	$109.80
Purchase #2	$192.35	8.357%	$208.4247	$208.42	$208.40	$208.40
Purchase #3	$113.57	6.804%	$121.2973	$121.30	$121.30	$121.30
Purchase #4	$241.56	11.603%	$269.5882	$269.59	$269.60	$269.60
Purchase #5	$152.54	9.841%	$167.5515	$167.55	$167.55	$167.60
Purchase #6	$48.39	11.408%	$53.9103	$53.91	$53.90	$53.90
Purchase #7	$134.32	10.549%	$148.4894	$148.49	$148.50	$148.50
7 purchase totals =	$983.14		$1,079.0557	$1,079.05	$1,079.05	$1,079.10