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	$81.74	6.822%	$87.3163	$87.32	$87.30	$87.30
Purchase #2	$173.50	12.358%	$194.9411	$194.94	$194.95	$194.90
Purchase #3	$35.25	10.384%	$38.9104	$38.91	$38.90	$38.90
Purchase #4	$10.65	13.846%	$12.1246	$12.12	$12.10	$12.10
Purchase #5	$103.68	5.555%	$109.4394	$109.44	$109.45	$109.40
Purchase #6	$43.84	3.391%	$45.3266	$45.33	$45.35	$45.30
Purchase #7	$85.44	6.134%	$90.6809	$90.68	$90.70	$90.70
7 purchase totals =	$534.10		$578.7393	$578.74	$578.75	$578.60