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	$146.25	9.429%	$160.0399	$160.04	$160.05	$160.00
Purchase #2	$99.51	10.542%	$110.0003	$110.00	$110.00	$110.00
Purchase #3	$145.32	9.113%	$158.563	$158.56	$158.55	$158.60
Purchase #4	$125.84	12.728%	$141.8569	$141.86	$141.85	$141.90
Purchase #5	$98.81	13.655%	$112.3025	$112.30	$112.30	$112.30
Purchase #6	$246.83	7.185%	$264.5647	$264.56	$264.55	$264.60
Purchase #7	$46.46	8.865%	$50.5787	$50.58	$50.60	$50.60
7 purchase totals =	$909.02		$997.9060	$997.90	$997.90	$998.00