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	$108.34	6.861%	$115.7732	$115.77	$115.75	$115.80
Purchase #2	$82.57	9.476%	$90.3943	$90.39	$90.40	$90.40
Purchase #3	$152.51	11.143%	$169.5042	$169.50	$169.50	$169.50
Purchase #4	$19.69	10.349%	$21.7277	$21.73	$21.75	$21.70
Purchase #5	$139.37	13.576%	$158.2909	$158.29	$158.30	$158.30
Purchase #6	$224.47	10.847%	$248.8183	$248.82	$248.80	$248.80
Purchase #7	$86.45	3.797%	$89.7325	$89.73	$89.75	$89.70
7 purchase totals =	$813.40		$894.2411	$894.23	$894.25	$894.20