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	$243.62	12.206%	$273.3563	$273.36	$273.35	$273.40
Purchase #2	$149.45	4.874%	$156.7342	$156.73	$156.75	$156.70
Purchase #3	$112.37	6.322%	$119.474	$119.47	$119.45	$119.50
Purchase #4	$99.93	3.155%	$103.0828	$103.08	$103.10	$103.10
Purchase #5	$91.33	8.757%	$99.3278	$99.33	$99.35	$99.30
Purchase #6	$163.28	3.509%	$169.0095	$169.01	$169.00	$169.00
Purchase #7	$90.30	4.480%	$94.3454	$94.35	$94.35	$94.30
7 purchase totals =	$950.28		$1,015.3300	$1,015.33	$1,015.35	$1,015.30