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	$25.45	6.498%	$27.1037	$27.10	$27.10	$27.10
Purchase #2	$75.39	9.721%	$82.7187	$82.72	$82.70	$82.70
Purchase #3	$222.37	8.637%	$241.5761	$241.58	$241.60	$241.60
Purchase #4	$142.91	3.781%	$148.3134	$148.31	$148.30	$148.30
Purchase #5	$191.45	10.344%	$211.2536	$211.25	$211.25	$211.30
Purchase #6	$33.43	9.330%	$36.549	$36.55	$36.55	$36.50
Purchase #7	$105.55	13.290%	$119.5776	$119.58	$119.60	$119.60
7 purchase totals =	$796.55		$867.0921	$867.09	$867.10	$867.10