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	$75.39	4.665%	$78.9069	$78.91	$78.90	$78.90
Purchase #2	$224.91	13.449%	$255.1581	$255.16	$255.15	$255.20
Purchase #3	$79.32	9.645%	$86.9704	$86.97	$86.95	$87.00
Purchase #4	$167.32	10.228%	$184.4335	$184.43	$184.45	$184.40
Purchase #5	$15.54	13.538%	$17.6438	$17.64	$17.65	$17.60
Purchase #6	$135.65	5.218%	$142.7282	$142.73	$142.75	$142.70
Purchase #7	$53.81	11.441%	$59.9664	$59.97	$59.95	$60.00
7 purchase totals =	$751.94		$825.8073	$825.81	$825.80	$825.80