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	$170.36	4.798%	$178.5339	$178.53	$178.55	$178.50
Purchase #2	$196.33	6.851%	$209.7806	$209.78	$209.80	$209.80
Purchase #3	$75.68	6.147%	$80.332	$80.33	$80.35	$80.30
Purchase #4	$81.28	10.738%	$90.0078	$90.01	$90.00	$90.00
Purchase #5	$51.64	7.673%	$55.6023	$55.60	$55.60	$55.60
Purchase #6	$198.65	6.270%	$211.1054	$211.11	$211.10	$211.10
Purchase #7	$141.82	4.525%	$148.2374	$148.24	$148.25	$148.20
7 purchase totals =	$915.76		$973.5994	$973.60	$973.65	$973.50