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	$232.37	9.509%	$254.4661	$254.47	$254.45	$254.50
Purchase #2	$38.30	7.371%	$41.1231	$41.12	$41.10	$41.10
Purchase #3	$80.59	5.673%	$85.1619	$85.16	$85.15	$85.20
Purchase #4	$177.77	6.635%	$189.565	$189.57	$189.55	$189.60
Purchase #5	$13.89	11.608%	$15.5024	$15.50	$15.50	$15.50
Purchase #6	$19.56	7.793%	$21.0843	$21.08	$21.10	$21.10
Purchase #7	$65.44	3.214%	$67.5432	$67.54	$67.55	$67.50
7 purchase totals =	$627.92		$674.4460	$674.44	$674.40	$674.50