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	$72.28	4.286%	$75.3779	$75.38	$75.40	$75.40
Purchase #2	$203.47	11.380%	$226.6249	$226.62	$226.60	$226.60
Purchase #3	$19.88	11.401%	$22.1465	$22.15	$22.15	$22.10
Purchase #4	$75.39	10.337%	$83.1831	$83.18	$83.20	$83.20
Purchase #5	$157.91	10.392%	$174.32	$174.32	$174.30	$174.30
Purchase #6	$57.57	3.327%	$59.4854	$59.49	$59.50	$59.50
Purchase #7	$131.82	5.616%	$139.223	$139.22	$139.20	$139.20
7 purchase totals =	$718.32		$780.3608	$780.36	$780.35	$780.30