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	$126.90	7.611%	$136.5584	$136.56	$136.55	$136.60
Purchase #2	$136.36	3.381%	$140.9703	$140.97	$140.95	$141.00
Purchase #3	$51.47	13.258%	$58.2939	$58.29	$58.30	$58.30
Purchase #4	$42.27	6.578%	$45.0505	$45.05	$45.05	$45.10
Purchase #5	$49.41	4.257%	$51.5134	$51.51	$51.50	$51.50
Purchase #6	$80.69	7.141%	$86.4521	$86.45	$86.45	$86.50
Purchase #7	$93.70	12.742%	$105.6393	$105.64	$105.65	$105.60
7 purchase totals =	$580.80		$624.4779	$624.47	$624.45	$624.60