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	$249.58	12.343%	$280.3857	$280.39	$280.40	$280.40
Purchase #2	$119.65	12.436%	$134.5297	$134.53	$134.55	$134.50
Purchase #3	$96.29	6.416%	$102.468	$102.47	$102.45	$102.50
Purchase #4	$42.34	7.440%	$45.4901	$45.49	$45.50	$45.50
Purchase #5	$241.53	5.272%	$254.2635	$254.26	$254.25	$254.30
Purchase #6	$124.37	13.741%	$141.4597	$141.46	$141.45	$141.50
Purchase #7	$96.74	8.786%	$105.2396	$105.24	$105.25	$105.20
7 purchase totals =	$970.50		$1,063.8363	$1,063.84	$1,063.85	$1,063.90