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	$249.93	12.208%	$280.4415	$280.44	$280.45	$280.40
Purchase #2	$92.46	3.521%	$95.7155	$95.72	$95.70	$95.70
Purchase #3	$192.42	4.418%	$200.9211	$200.92	$200.90	$200.90
Purchase #4	$194.98	7.131%	$208.884	$208.88	$208.90	$208.90
Purchase #5	$71.59	13.791%	$81.463	$81.46	$81.45	$81.50
Purchase #6	$196.69	5.739%	$207.978	$207.98	$208.00	$208.00
Purchase #7	$158.72	9.601%	$173.9587	$173.96	$173.95	$174.00
7 purchase totals =	$1,156.79		$1,249.3618	$1,249.36	$1,249.35	$1,249.40