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	$45.79	12.434%	$51.4835	$51.48	$51.50	$51.50
Purchase #2	$69.95	12.233%	$78.507	$78.51	$78.50	$78.50
Purchase #3	$102.99	10.600%	$113.9069	$113.91	$113.90	$113.90
Purchase #4	$164.57	9.507%	$180.2157	$180.22	$180.20	$180.20
Purchase #5	$163.60	5.839%	$173.1526	$173.15	$173.15	$173.20
Purchase #6	$19.48	10.345%	$21.4952	$21.50	$21.50	$21.50
Purchase #7	$5.96	9.256%	$6.5117	$6.51	$6.50	$6.50
7 purchase totals =	$572.34		$625.2726	$625.28	$625.25	$625.30