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	$138.43	9.432%	$151.4867	$151.49	$151.50	$151.50
Purchase #2	$98.30	11.338%	$109.4453	$109.45	$109.45	$109.40
Purchase #3	$213.82	12.152%	$239.8034	$239.80	$239.80	$239.80
Purchase #4	$48.81	13.656%	$55.4755	$55.48	$55.50	$55.50
Purchase #5	$48.26	12.405%	$54.2467	$54.25	$54.25	$54.20
Purchase #6	$168.33	12.151%	$188.7838	$188.78	$188.80	$188.80
Purchase #7	$35.35	9.597%	$38.7425	$38.74	$38.75	$38.70
7 purchase totals =	$751.30		$837.9839	$837.99	$838.05	$837.90