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	$131.67	12.786%	$148.5053	$148.51	$148.50	$148.50
Purchase #2	$199.83	6.670%	$213.1587	$213.16	$213.15	$213.20
Purchase #3	$71.55	12.780%	$80.6941	$80.69	$80.70	$80.70
Purchase #4	$250.41	13.506%	$284.2304	$284.23	$284.25	$284.20
Purchase #5	$131.52	4.472%	$137.4016	$137.40	$137.40	$137.40
Purchase #6	$174.25	8.691%	$189.3941	$189.39	$189.40	$189.40
Purchase #7	$50.39	3.276%	$52.0408	$52.04	$52.05	$52.00
7 purchase totals =	$1,009.62		$1,105.4250	$1,105.42	$1,105.45	$1,105.40