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	$74.98	7.832%	$80.8524	$80.85	$80.85	$80.90
Purchase #2	$249.28	5.213%	$262.275	$262.28	$262.30	$262.30
Purchase #3	$81.58	12.277%	$91.5956	$91.60	$91.60	$91.60
Purchase #4	$135.55	11.406%	$151.0108	$151.01	$151.00	$151.00
Purchase #5	$6.44	8.787%	$7.0059	$7.01	$7.00	$7.00
Purchase #6	$171.89	8.475%	$186.4577	$186.46	$186.45	$186.50
Purchase #7	$59.58	12.256%	$66.8821	$66.88	$66.90	$66.90
7 purchase totals =	$779.30		$846.0795	$846.09	$846.10	$846.20