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	$177.69	12.355%	$199.6436	$199.64	$199.65	$199.60
Purchase #2	$73.90	11.802%	$82.6217	$82.62	$82.60	$82.60
Purchase #3	$234.74	13.498%	$266.4252	$266.43	$266.45	$266.40
Purchase #4	$69.91	4.649%	$73.1601	$73.16	$73.15	$73.20
Purchase #5	$176.99	7.752%	$190.7103	$190.71	$190.70	$190.70
Purchase #6	$32.43	9.767%	$35.5974	$35.60	$35.60	$35.60
Purchase #7	$151.98	13.559%	$172.587	$172.59	$172.60	$172.60
7 purchase totals =	$917.64		$1,020.7453	$1,020.75	$1,020.75	$1,020.70