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	$248.97	12.697%	$280.5817	$280.58	$280.60	$280.60
Purchase #2	$90.28	11.185%	$100.3778	$100.38	$100.40	$100.40
Purchase #3	$109.98	11.272%	$122.3769	$122.38	$122.40	$122.40
Purchase #4	$250.78	3.472%	$259.4871	$259.49	$259.50	$259.50
Purchase #5	$84.44	6.321%	$89.7775	$89.78	$89.80	$89.80
Purchase #6	$92.47	6.862%	$98.8153	$98.82	$98.80	$98.80
Purchase #7	$157.28	5.407%	$165.7841	$165.78	$165.80	$165.80
7 purchase totals =	$1,034.20		$1,117.2004	$1,117.21	$1,117.30	$1,117.30