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	$101.43	8.260%	$109.8081	$109.81	$109.80	$109.80
Purchase #2	$112.90	12.337%	$126.8285	$126.83	$126.85	$126.80
Purchase #3	$89.79	12.309%	$100.8423	$100.84	$100.85	$100.80
Purchase #4	$161.36	10.254%	$177.9059	$177.91	$177.90	$177.90
Purchase #5	$137.64	9.212%	$150.3194	$150.32	$150.30	$150.30
Purchase #6	$52.81	10.616%	$58.4163	$58.42	$58.40	$58.40
Purchase #7	$42.90	12.140%	$48.1081	$48.11	$48.10	$48.10
7 purchase totals =	$698.83		$772.2286	$772.24	$772.20	$772.10