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	$85.53	6.294%	$90.9133	$90.91	$90.90	$90.90
Purchase #2	$131.91	9.515%	$144.4612	$144.46	$144.45	$144.50
Purchase #3	$187.25	9.434%	$204.9152	$204.92	$204.90	$204.90
Purchase #4	$40.47	11.129%	$44.9739	$44.97	$44.95	$45.00
Purchase #5	$53.90	8.704%	$58.5915	$58.59	$58.60	$58.60
Purchase #6	$131.50	12.174%	$147.5088	$147.51	$147.50	$147.50
Purchase #7	$119.64	11.504%	$133.4034	$133.40	$133.40	$133.40
7 purchase totals =	$750.20		$824.7673	$824.76	$824.70	$824.80