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	$101.31	8.456%	$109.8768	$109.88	$109.90	$109.90
Purchase #2	$7.61	4.781%	$7.9738	$7.97	$7.95	$8.00
Purchase #3	$175.60	7.239%	$188.3117	$188.31	$188.30	$188.30
Purchase #4	$16.75	12.664%	$18.8712	$18.87	$18.85	$18.90
Purchase #5	$31.53	11.301%	$35.0932	$35.09	$35.10	$35.10
Purchase #6	$80.38	11.254%	$89.426	$89.43	$89.45	$89.40
Purchase #7	$102.89	9.108%	$112.2612	$112.26	$112.25	$112.30
7 purchase totals =	$516.07		$561.8139	$561.81	$561.80	$561.90