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	$27.88	12.738%	$31.4314	$31.43	$31.45	$31.40
Purchase #2	$96.51	5.662%	$101.9744	$101.97	$101.95	$102.00
Purchase #3	$250.58	7.383%	$269.0803	$269.08	$269.10	$269.10
Purchase #4	$78.51	8.862%	$85.4676	$85.47	$85.45	$85.50
Purchase #5	$250.93	5.321%	$264.282	$264.28	$264.30	$264.30
Purchase #6	$28.99	9.746%	$31.8154	$31.82	$31.80	$31.80
Purchase #7	$239.82	3.635%	$248.5375	$248.54	$248.55	$248.50
7 purchase totals =	$973.22		$1,032.5886	$1,032.59	$1,032.60	$1,032.60