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	$163.74	13.359%	$185.614	$185.61	$185.60	$185.60
Purchase #2	$58.91	6.504%	$62.7415	$62.74	$62.75	$62.70
Purchase #3	$37.97	10.621%	$42.0028	$42.00	$42.00	$42.00
Purchase #4	$86.88	8.609%	$94.3595	$94.36	$94.35	$94.40
Purchase #5	$214.65	3.813%	$222.8346	$222.83	$222.85	$222.80
Purchase #6	$5.81	9.497%	$6.3618	$6.36	$6.35	$6.40
Purchase #7	$51.35	4.516%	$53.669	$53.67	$53.65	$53.70
7 purchase totals =	$619.31		$667.5832	$667.57	$667.55	$667.60