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	$33.49	6.267%	$35.5888	$35.59	$35.60	$35.60
Purchase #2	$38.78	9.595%	$42.5009	$42.50	$42.50	$42.50
Purchase #3	$226.40	4.646%	$236.9185	$236.92	$236.90	$236.90
Purchase #4	$145.89	7.557%	$156.9149	$156.91	$156.90	$156.90
Purchase #5	$66.38	7.769%	$71.5371	$71.54	$71.55	$71.50
Purchase #6	$228.54	5.832%	$241.8685	$241.87	$241.85	$241.90
Purchase #7	$80.86	9.377%	$88.4422	$88.44	$88.45	$88.40
7 purchase totals =	$820.34		$873.7709	$873.77	$873.75	$873.70