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	$14.55	9.156%	$15.8822	$15.88	$15.90	$15.90
Purchase #2	$87.27	13.713%	$99.2373	$99.24	$99.25	$99.20
Purchase #3	$37.74	12.166%	$42.3314	$42.33	$42.35	$42.30
Purchase #4	$28.99	12.527%	$32.6216	$32.62	$32.60	$32.60
Purchase #5	$67.68	7.499%	$72.7553	$72.76	$72.75	$72.80
Purchase #6	$221.51	4.758%	$232.0494	$232.05	$232.05	$232.00
Purchase #7	$43.65	5.576%	$46.0839	$46.08	$46.10	$46.10
7 purchase totals =	$501.39		$540.9611	$540.96	$541.00	$540.90