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	$39.75	13.537%	$45.131	$45.13	$45.15	$45.10
Purchase #2	$136.62	3.366%	$141.2186	$141.22	$141.20	$141.20
Purchase #3	$142.88	7.243%	$153.2288	$153.23	$153.25	$153.20
Purchase #4	$14.89	3.252%	$15.3742	$15.37	$15.35	$15.40
Purchase #5	$7.51	3.660%	$7.7849	$7.78	$7.80	$7.80
Purchase #6	$136.47	3.256%	$140.9135	$140.91	$140.90	$140.90
Purchase #7	$128.74	13.615%	$146.268	$146.27	$146.25	$146.30
7 purchase totals =	$606.86		$649.9190	$649.91	$649.90	$649.90