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	$72.56	8.704%	$78.8756	$78.88	$78.90	$78.90
Purchase #2	$123.58	6.278%	$131.3384	$131.34	$131.35	$131.30
Purchase #3	$70.95	13.717%	$80.6822	$80.68	$80.70	$80.70
Purchase #4	$152.89	9.835%	$167.9267	$167.93	$167.95	$167.90
Purchase #5	$56.36	4.551%	$58.9249	$58.92	$58.90	$58.90
Purchase #6	$211.44	12.158%	$237.1469	$237.15	$237.15	$237.10
Purchase #7	$131.95	11.405%	$146.9989	$147.00	$147.00	$147.00
7 purchase totals =	$819.73		$901.8936	$901.90	$901.95	$901.80