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	$29.73	5.208%	$31.2783	$31.28	$31.30	$31.30
Purchase #2	$145.80	4.631%	$152.552	$152.55	$152.55	$152.60
Purchase #3	$70.57	9.340%	$77.1612	$77.16	$77.15	$77.20
Purchase #4	$20.27	8.233%	$21.9388	$21.94	$21.95	$21.90
Purchase #5	$90.79	6.791%	$96.9555	$96.96	$96.95	$97.00
Purchase #6	$198.88	12.872%	$224.4798	$224.48	$224.50	$224.50
Purchase #7	$188.99	3.825%	$196.2189	$196.22	$196.20	$196.20
7 purchase totals =	$745.03		$800.5845	$800.59	$800.60	$800.70