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	$20.35	10.717%	$22.5309	$22.53	$22.55	$22.50
Purchase #2	$55.49	8.454%	$60.1811	$60.18	$60.20	$60.20
Purchase #3	$223.70	7.745%	$241.0256	$241.03	$241.05	$241.00
Purchase #4	$58.66	11.781%	$65.5707	$65.57	$65.55	$65.60
Purchase #5	$168.46	12.434%	$189.4063	$189.41	$189.40	$189.40
Purchase #6	$36.65	10.226%	$40.3978	$40.40	$40.40	$40.40
Purchase #7	$27.73	13.308%	$31.4203	$31.42	$31.40	$31.40
7 purchase totals =	$591.04		$650.5327	$650.54	$650.55	$650.50