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	$171.46	6.435%	$182.4935	$182.49	$182.50	$182.50
Purchase #2	$249.52	12.253%	$280.0937	$280.09	$280.10	$280.10
Purchase #3	$173.67	7.115%	$186.0266	$186.03	$186.05	$186.00
Purchase #4	$127.38	9.287%	$139.2098	$139.21	$139.20	$139.20
Purchase #5	$121.77	4.597%	$127.3678	$127.37	$127.35	$127.40
Purchase #6	$105.97	12.797%	$119.531	$119.53	$119.55	$119.50
Purchase #7	$161.33	6.847%	$172.3763	$172.38	$172.40	$172.40
7 purchase totals =	$1,111.10		$1,207.0987	$1,207.10	$1,207.15	$1,207.10