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	$204.98	6.781%	$218.8797	$218.88	$218.90	$218.90
Purchase #2	$169.34	12.247%	$190.0791	$190.08	$190.10	$190.10
Purchase #3	$188.50	11.365%	$209.923	$209.92	$209.90	$209.90
Purchase #4	$94.40	5.721%	$99.8006	$99.80	$99.80	$99.80
Purchase #5	$194.60	4.402%	$203.1663	$203.17	$203.15	$203.20
Purchase #6	$136.90	11.784%	$153.0323	$153.03	$153.05	$153.00
Purchase #7	$150.82	3.541%	$156.1605	$156.16	$156.15	$156.20
7 purchase totals =	$1,139.54		$1,231.0415	$1,231.04	$1,231.05	$1,231.10