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	$92.52	11.779%	$103.4179	$103.42	$103.40	$103.40
Purchase #2	$49.81	11.508%	$55.5421	$55.54	$55.55	$55.50
Purchase #3	$118.38	11.426%	$131.9061	$131.91	$131.90	$131.90
Purchase #4	$137.44	9.430%	$150.4006	$150.40	$150.40	$150.40
Purchase #5	$20.29	7.551%	$21.8221	$21.82	$21.80	$21.80
Purchase #6	$96.86	5.228%	$101.9238	$101.92	$101.90	$101.90
Purchase #7	$196.80	6.314%	$209.226	$209.23	$209.25	$209.20
7 purchase totals =	$712.10		$774.2386	$774.24	$774.20	$774.10