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	$59.62	12.513%	$67.0803	$67.08	$67.10	$67.10
Purchase #2	$160.37	7.159%	$171.8509	$171.85	$171.85	$171.90
Purchase #3	$128.89	9.423%	$141.0353	$141.04	$141.05	$141.00
Purchase #4	$81.85	12.236%	$91.8652	$91.87	$91.85	$91.90
Purchase #5	$87.98	13.196%	$99.5898	$99.59	$99.60	$99.60
Purchase #6	$54.66	5.332%	$57.5745	$57.57	$57.55	$57.60
Purchase #7	$129.80	6.106%	$137.7256	$137.73	$137.75	$137.70
7 purchase totals =	$703.17		$766.7216	$766.73	$766.75	$766.80