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	$8.95	4.113%	$9.3181	$9.32	$9.30	$9.30
Purchase #2	$167.79	5.823%	$177.5604	$177.56	$177.55	$177.60
Purchase #3	$89.26	11.380%	$99.4178	$99.42	$99.40	$99.40
Purchase #4	$121.92	7.765%	$131.3871	$131.39	$131.40	$131.40
Purchase #5	$56.26	5.699%	$59.4663	$59.47	$59.45	$59.50
Purchase #6	$32.36	3.127%	$33.3719	$33.37	$33.35	$33.40
Purchase #7	$143.50	7.681%	$154.5222	$154.52	$154.50	$154.50
7 purchase totals =	$620.04		$665.0438	$665.05	$664.95	$665.10