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	$174.75	8.431%	$189.4832	$189.48	$189.50	$189.50
Purchase #2	$239.62	13.418%	$271.7722	$271.77	$271.75	$271.80
Purchase #3	$92.32	12.619%	$103.9699	$103.97	$103.95	$104.00
Purchase #4	$240.44	6.611%	$256.3355	$256.34	$256.35	$256.30
Purchase #5	$91.80	11.354%	$102.223	$102.22	$102.20	$102.20
Purchase #6	$9.28	12.294%	$10.4209	$10.42	$10.40	$10.40
Purchase #7	$52.60	12.796%	$59.3307	$59.33	$59.35	$59.30
7 purchase totals =	$900.81		$993.5354	$993.53	$993.50	$993.50