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	$223.48	6.700%	$238.4532	$238.45	$238.45	$238.50
Purchase #2	$74.82	9.784%	$82.1404	$82.14	$82.15	$82.10
Purchase #3	$216.50	11.122%	$240.5791	$240.58	$240.60	$240.60
Purchase #4	$200.33	11.276%	$222.9192	$222.92	$222.90	$222.90
Purchase #5	$73.89	9.187%	$80.6783	$80.68	$80.70	$80.70
Purchase #6	$151.59	4.824%	$158.9027	$158.90	$158.90	$158.90
Purchase #7	$237.69	9.793%	$260.967	$260.97	$260.95	$261.00
7 purchase totals =	$1,178.30		$1,284.6399	$1,284.64	$1,284.65	$1,284.70