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	$20.38	13.104%	$23.0506	$23.05	$23.05	$23.10
Purchase #2	$168.30	12.614%	$189.5294	$189.53	$189.55	$189.50
Purchase #3	$48.38	11.397%	$53.8939	$53.89	$53.90	$53.90
Purchase #4	$53.69	5.358%	$56.5667	$56.57	$56.55	$56.60
Purchase #5	$131.32	7.464%	$141.1217	$141.12	$141.10	$141.10
Purchase #6	$55.92	5.117%	$58.7814	$58.78	$58.80	$58.80
Purchase #7	$231.32	10.186%	$254.8823	$254.88	$254.90	$254.90
7 purchase totals =	$709.31		$777.8260	$777.82	$777.85	$777.90