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	$86.80	6.244%	$92.2198	$92.22	$92.20	$92.20
Purchase #2	$108.50	4.161%	$113.0147	$113.01	$113.00	$113.00
Purchase #3	$50.40	9.696%	$55.2868	$55.29	$55.30	$55.30
Purchase #4	$140.32	12.543%	$157.9203	$157.92	$157.90	$157.90
Purchase #5	$108.70	5.343%	$114.5078	$114.51	$114.50	$114.50
Purchase #6	$139.83	10.835%	$154.9806	$154.98	$155.00	$155.00
Purchase #7	$100.61	11.757%	$112.4387	$112.44	$112.45	$112.40
7 purchase totals =	$735.16		$800.3687	$800.37	$800.35	$800.30