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	$141.87	6.320%	$150.8362	$150.84	$150.85	$150.80
Purchase #2	$100.66	9.672%	$110.3958	$110.40	$110.40	$110.40
Purchase #3	$90.95	9.270%	$99.3811	$99.38	$99.40	$99.40
Purchase #4	$99.32	3.556%	$102.8518	$102.85	$102.85	$102.90
Purchase #5	$88.95	13.417%	$100.8844	$100.88	$100.90	$100.90
Purchase #6	$200.49	10.730%	$222.0026	$222.00	$222.00	$222.00
Purchase #7	$137.60	11.742%	$153.757	$153.76	$153.75	$153.80
7 purchase totals =	$859.84		$940.1089	$940.11	$940.15	$940.20