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	$32.83	12.514%	$36.9383	$36.94	$36.95	$36.90
Purchase #2	$230.72	7.698%	$248.4808	$248.48	$248.50	$248.50
Purchase #3	$147.94	9.871%	$162.5432	$162.54	$162.55	$162.50
Purchase #4	$130.32	12.363%	$146.4315	$146.43	$146.45	$146.40
Purchase #5	$73.48	9.677%	$80.5907	$80.59	$80.60	$80.60
Purchase #6	$128.45	9.591%	$140.7696	$140.77	$140.75	$140.80
Purchase #7	$240.89	4.114%	$250.8002	$250.80	$250.80	$250.80
7 purchase totals =	$984.63		$1,066.5543	$1,066.55	$1,066.60	$1,066.50