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	$248.25	12.722%	$279.8324	$279.83	$279.85	$279.80
Purchase #2	$111.66	5.258%	$117.5311	$117.53	$117.55	$117.50
Purchase #3	$134.95	3.180%	$139.2414	$139.24	$139.25	$139.20
Purchase #4	$96.86	4.125%	$100.8555	$100.86	$100.85	$100.90
Purchase #5	$21.45	12.806%	$24.1969	$24.20	$24.20	$24.20
Purchase #6	$187.53	11.190%	$208.5146	$208.51	$208.50	$208.50
Purchase #7	$213.76	4.591%	$223.5737	$223.57	$223.55	$223.60
7 purchase totals =	$1,014.46		$1,093.7456	$1,093.74	$1,093.75	$1,093.70