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	$88.44	3.330%	$91.3851	$91.39	$91.40	$91.40
Purchase #2	$221.98	3.151%	$228.9746	$228.97	$228.95	$229.00
Purchase #3	$9.92	9.778%	$10.89	$10.89	$10.90	$10.90
Purchase #4	$91.25	12.685%	$102.8251	$102.83	$102.85	$102.80
Purchase #5	$90.37	9.799%	$99.2254	$99.23	$99.25	$99.20
Purchase #6	$44.76	11.327%	$49.83	$49.83	$49.85	$49.80
Purchase #7	$10.97	6.398%	$11.6719	$11.67	$11.65	$11.70
7 purchase totals =	$557.69		$594.8021	$594.81	$594.85	$594.80