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	$185.62	3.370%	$191.8754	$191.88	$191.90	$191.90
Purchase #2	$113.45	5.378%	$119.5513	$119.55	$119.55	$119.60
Purchase #3	$138.39	10.414%	$152.8019	$152.80	$152.80	$152.80
Purchase #4	$112.89	9.699%	$123.8392	$123.84	$123.85	$123.80
Purchase #5	$103.28	7.676%	$111.2078	$111.21	$111.20	$111.20
Purchase #6	$160.83	11.487%	$179.3045	$179.30	$179.30	$179.30
Purchase #7	$24.85	13.843%	$28.29	$28.29	$28.30	$28.30
7 purchase totals =	$839.31		$906.8701	$906.87	$906.90	$906.90