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	$167.69	7.823%	$180.8084	$180.81	$180.80	$180.80
Purchase #2	$85.77	11.835%	$95.9209	$95.92	$95.90	$95.90
Purchase #3	$91.30	13.333%	$103.473	$103.47	$103.45	$103.50
Purchase #4	$155.50	8.260%	$168.3443	$168.34	$168.35	$168.30
Purchase #5	$31.61	9.456%	$34.599	$34.60	$34.60	$34.60
Purchase #6	$108.73	6.480%	$115.7757	$115.78	$115.80	$115.80
Purchase #7	$150.64	11.321%	$167.694	$167.69	$167.70	$167.70
7 purchase totals =	$791.24		$866.6153	$866.61	$866.60	$866.60