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	$19.79	13.804%	$22.5218	$22.52	$22.50	$22.50
Purchase #2	$162.44	13.819%	$184.8876	$184.89	$184.90	$184.90
Purchase #3	$181.28	11.197%	$201.5779	$201.58	$201.60	$201.60
Purchase #4	$41.28	9.766%	$45.3114	$45.31	$45.30	$45.30
Purchase #5	$35.95	7.347%	$38.5912	$38.59	$38.60	$38.60
Purchase #6	$246.57	3.780%	$255.8903	$255.89	$255.90	$255.90
Purchase #7	$62.99	12.420%	$70.8134	$70.81	$70.80	$70.80
7 purchase totals =	$750.30		$819.5936	$819.59	$819.60	$819.60