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	$11.88	6.862%	$12.6952	$12.70	$12.70	$12.70
Purchase #2	$97.30	3.340%	$100.5498	$100.55	$100.55	$100.50
Purchase #3	$248.92	12.668%	$280.4532	$280.45	$280.45	$280.50
Purchase #4	$240.96	6.298%	$256.1357	$256.14	$256.15	$256.10
Purchase #5	$37.61	12.667%	$42.3741	$42.37	$42.35	$42.40
Purchase #6	$52.40	3.308%	$54.1334	$54.13	$54.15	$54.10
Purchase #7	$218.75	6.370%	$232.6844	$232.68	$232.70	$232.70
7 purchase totals =	$907.82		$979.0258	$979.02	$979.05	$979.00