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	$36.74	6.851%	$39.2571	$39.26	$39.25	$39.30
Purchase #2	$176.83	8.852%	$192.483	$192.48	$192.50	$192.50
Purchase #3	$56.89	12.194%	$63.8272	$63.83	$63.85	$63.80
Purchase #4	$38.30	6.364%	$40.7374	$40.74	$40.75	$40.70
Purchase #5	$131.96	9.231%	$144.1412	$144.14	$144.15	$144.10
Purchase #6	$160.76	6.648%	$171.4473	$171.45	$171.45	$171.40
Purchase #7	$139.85	4.701%	$146.4243	$146.42	$146.40	$146.40
7 purchase totals =	$741.33		$798.3175	$798.32	$798.35	$798.20