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	$14.31	12.855%	$16.1496	$16.15	$16.15	$16.10
Purchase #2	$131.40	10.572%	$145.2916	$145.29	$145.30	$145.30
Purchase #3	$250.65	11.740%	$280.0763	$280.08	$280.10	$280.10
Purchase #4	$213.46	11.826%	$238.7038	$238.70	$238.70	$238.70
Purchase #5	$175.91	4.328%	$183.5234	$183.52	$183.50	$183.50
Purchase #6	$29.63	12.751%	$33.4081	$33.41	$33.40	$33.40
Purchase #7	$40.55	4.855%	$42.5187	$42.52	$42.50	$42.50
7 purchase totals =	$855.91		$939.6715	$939.67	$939.65	$939.60