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	$78.89	13.862%	$89.8257	$89.83	$89.85	$89.80
Purchase #2	$42.54	4.319%	$44.3773	$44.38	$44.40	$44.40
Purchase #3	$200.25	4.303%	$208.8668	$208.87	$208.85	$208.90
Purchase #4	$212.27	12.389%	$238.5681	$238.57	$238.55	$238.60
Purchase #5	$73.94	9.280%	$80.8016	$80.80	$80.80	$80.80
Purchase #6	$36.45	5.124%	$38.3177	$38.32	$38.30	$38.30
Purchase #7	$185.85	12.660%	$209.3786	$209.38	$209.40	$209.40
7 purchase totals =	$830.19		$910.1358	$910.15	$910.15	$910.20