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	$28.33	11.254%	$31.5183	$31.52	$31.50	$31.50
Purchase #2	$82.94	4.325%	$86.5272	$86.53	$86.55	$86.50
Purchase #3	$211.96	8.739%	$230.4832	$230.48	$230.50	$230.50
Purchase #4	$162.49	13.617%	$184.6163	$184.62	$184.60	$184.60
Purchase #5	$16.33	7.195%	$17.5049	$17.50	$17.50	$17.50
Purchase #6	$134.96	6.611%	$143.8822	$143.88	$143.90	$143.90
Purchase #7	$91.79	3.280%	$94.8007	$94.80	$94.80	$94.80
7 purchase totals =	$728.80		$789.3328	$789.33	$789.35	$789.30