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	$38.46	10.274%	$42.4114	$42.41	$42.40	$42.40
Purchase #2	$39.80	4.396%	$41.5496	$41.55	$41.55	$41.50
Purchase #3	$191.25	4.848%	$200.5218	$200.52	$200.50	$200.50
Purchase #4	$18.39	11.473%	$20.4999	$20.50	$20.50	$20.50
Purchase #5	$109.29	10.250%	$120.4922	$120.49	$120.50	$120.50
Purchase #6	$228.88	4.163%	$238.4083	$238.41	$238.40	$238.40
Purchase #7	$7.56	11.351%	$8.4181	$8.42	$8.40	$8.40
7 purchase totals =	$633.63		$672.3013	$672.30	$672.25	$672.20