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	$249.64	10.221%	$275.1557	$275.16	$275.15	$275.20
Purchase #2	$107.63	10.386%	$118.8085	$118.81	$118.80	$118.80
Purchase #3	$35.41	11.283%	$39.4053	$39.41	$39.40	$39.40
Purchase #4	$87.52	3.851%	$90.8904	$90.89	$90.90	$90.90
Purchase #5	$114.55	8.765%	$124.5903	$124.59	$124.60	$124.60
Purchase #6	$205.81	11.221%	$228.9039	$228.90	$228.90	$228.90
Purchase #7	$201.92	3.157%	$208.2946	$208.29	$208.30	$208.30
7 purchase totals =	$1,002.48		$1,086.0487	$1,086.05	$1,086.05	$1,086.10