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	$159.63	11.616%	$178.1726	$178.17	$178.15	$178.20
Purchase #2	$88.54	12.210%	$99.3507	$99.35	$99.35	$99.40
Purchase #3	$65.62	3.382%	$67.8393	$67.84	$67.85	$67.80
Purchase #4	$62.28	8.223%	$67.4013	$67.40	$67.40	$67.40
Purchase #5	$98.88	3.822%	$102.6592	$102.66	$102.65	$102.70
Purchase #6	$179.81	6.649%	$191.7656	$191.77	$191.75	$191.80
Purchase #7	$90.60	4.315%	$94.5094	$94.51	$94.50	$94.50
7 purchase totals =	$745.36		$801.6981	$801.70	$801.65	$801.80