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	$229.40	4.614%	$239.9845	$239.98	$240.00	$240.00
Purchase #2	$24.49	11.206%	$27.2343	$27.23	$27.25	$27.20
Purchase #3	$76.93	13.280%	$87.1463	$87.15	$87.15	$87.10
Purchase #4	$134.74	5.459%	$142.0955	$142.10	$142.10	$142.10
Purchase #5	$250.49	12.785%	$282.5151	$282.52	$282.50	$282.50
Purchase #6	$61.72	5.759%	$65.2745	$65.27	$65.25	$65.30
Purchase #7	$244.96	4.574%	$256.1645	$256.16	$256.15	$256.20
7 purchase totals =	$1,022.73		$1,100.4147	$1,100.41	$1,100.40	$1,100.40