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	$206.90	7.121%	$221.6333	$221.63	$221.65	$221.60
Purchase #2	$250.43	6.141%	$265.8089	$265.81	$265.80	$265.80
Purchase #3	$156.98	10.588%	$173.601	$173.60	$173.60	$173.60
Purchase #4	$103.85	12.490%	$116.8209	$116.82	$116.80	$116.80
Purchase #5	$148.48	7.288%	$159.3012	$159.30	$159.30	$159.30
Purchase #6	$27.65	13.623%	$31.4168	$31.42	$31.40	$31.40
Purchase #7	$74.74	9.708%	$81.9958	$82.00	$82.00	$82.00
7 purchase totals =	$969.03		$1,050.5779	$1,050.58	$1,050.55	$1,050.50