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	$199.72	7.728%	$215.1544	$215.15	$215.15	$215.20
Purchase #2	$85.54	12.344%	$96.0991	$96.10	$96.10	$96.10
Purchase #3	$157.93	11.434%	$175.9877	$175.99	$176.00	$176.00
Purchase #4	$155.41	9.415%	$170.0419	$170.04	$170.05	$170.00
Purchase #5	$13.89	13.215%	$15.7256	$15.73	$15.75	$15.70
Purchase #6	$117.44	11.763%	$131.2545	$131.25	$131.25	$131.30
Purchase #7	$39.72	6.520%	$42.3097	$42.31	$42.30	$42.30
7 purchase totals =	$769.65		$846.5729	$846.57	$846.60	$846.60