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	$81.48	12.496%	$91.6617	$91.66	$91.65	$91.70
Purchase #2	$50.69	11.479%	$56.5087	$56.51	$56.50	$56.50
Purchase #3	$73.70	6.203%	$78.2716	$78.27	$78.25	$78.30
Purchase #4	$108.66	9.861%	$119.375	$119.38	$119.40	$119.40
Purchase #5	$70.72	11.532%	$78.8754	$78.88	$78.90	$78.90
Purchase #6	$29.47	4.495%	$30.7947	$30.79	$30.80	$30.80
Purchase #7	$213.52	8.240%	$231.114	$231.11	$231.10	$231.10
7 purchase totals =	$628.24		$686.6011	$686.60	$686.60	$686.70