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	$143.50	3.444%	$148.4421	$148.44	$148.45	$148.40
Purchase #2	$40.64	10.674%	$44.9779	$44.98	$45.00	$45.00
Purchase #3	$130.51	6.336%	$138.7791	$138.78	$138.80	$138.80
Purchase #4	$35.43	9.833%	$38.9138	$38.91	$38.90	$38.90
Purchase #5	$92.58	3.249%	$95.5879	$95.59	$95.60	$95.60
Purchase #6	$45.51	10.157%	$50.1325	$50.13	$50.15	$50.10
Purchase #7	$31.73	5.807%	$33.5726	$33.57	$33.55	$33.60
7 purchase totals =	$519.90		$550.4059	$550.40	$550.45	$550.40