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	$134.43	4.708%	$140.759	$140.76	$140.75	$140.80
Purchase #2	$198.32	13.709%	$225.5077	$225.51	$225.50	$225.50
Purchase #3	$166.58	4.332%	$173.7962	$173.80	$173.80	$173.80
Purchase #4	$227.30	12.847%	$256.5012	$256.50	$256.50	$256.50
Purchase #5	$75.29	13.385%	$85.3676	$85.37	$85.35	$85.40
Purchase #6	$31.25	7.115%	$33.4734	$33.47	$33.45	$33.50
Purchase #7	$14.97	4.471%	$15.6393	$15.64	$15.65	$15.60
7 purchase totals =	$848.14		$931.0444	$931.05	$931.00	$931.10