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	$60.29	13.551%	$68.4599	$68.46	$68.45	$68.50
Purchase #2	$50.73	7.384%	$54.4759	$54.48	$54.50	$54.50
Purchase #3	$71.90	12.487%	$80.8782	$80.88	$80.90	$80.90
Purchase #4	$114.61	8.765%	$124.6556	$124.66	$124.65	$124.70
Purchase #5	$212.37	12.312%	$238.517	$238.52	$238.50	$238.50
Purchase #6	$155.98	10.805%	$172.8336	$172.83	$172.85	$172.80
Purchase #7	$218.88	12.558%	$246.367	$246.37	$246.35	$246.40
7 purchase totals =	$884.76		$986.1872	$986.20	$986.20	$986.30