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	$74.84	7.677%	$80.5855	$80.59	$80.60	$80.60
Purchase #2	$158.83	12.389%	$178.5074	$178.51	$178.50	$178.50
Purchase #3	$189.34	10.690%	$209.5804	$209.58	$209.60	$209.60
Purchase #4	$210.36	3.126%	$216.9359	$216.94	$216.95	$216.90
Purchase #5	$81.28	4.585%	$85.0067	$85.01	$85.00	$85.00
Purchase #6	$124.74	5.275%	$131.32	$131.32	$131.30	$131.30
Purchase #7	$206.79	9.172%	$225.7568	$225.76	$225.75	$225.80
7 purchase totals =	$1,046.18		$1,127.6927	$1,127.71	$1,127.70	$1,127.70