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	$123.46	11.301%	$137.4122	$137.41	$137.40	$137.40
Purchase #2	$220.80	9.493%	$241.7605	$241.76	$241.75	$241.80
Purchase #3	$30.43	5.755%	$32.1812	$32.18	$32.20	$32.20
Purchase #4	$77.57	10.524%	$85.7335	$85.73	$85.75	$85.70
Purchase #5	$30.29	6.670%	$32.3103	$32.31	$32.30	$32.30
Purchase #6	$27.31	12.483%	$30.7191	$30.72	$30.70	$30.70
Purchase #7	$39.48	4.593%	$41.2933	$41.29	$41.30	$41.30
7 purchase totals =	$549.34		$601.4101	$601.40	$601.40	$601.40