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	$115.90	11.163%	$128.8379	$128.84	$128.85	$128.80
Purchase #2	$144.34	10.818%	$159.9547	$159.95	$159.95	$160.00
Purchase #3	$98.81	11.612%	$110.2838	$110.28	$110.30	$110.30
Purchase #4	$119.52	10.242%	$131.7612	$131.76	$131.75	$131.80
Purchase #5	$75.60	9.561%	$82.8281	$82.83	$82.85	$82.80
Purchase #6	$130.33	7.777%	$140.4658	$140.47	$140.45	$140.50
Purchase #7	$13.82	10.270%	$15.2393	$15.24	$15.25	$15.20
7 purchase totals =	$698.32		$769.3708	$769.37	$769.40	$769.40