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	$80.68	4.452%	$84.2719	$84.27	$84.25	$84.30
Purchase #2	$218.44	4.181%	$227.573	$227.57	$227.55	$227.60
Purchase #3	$180.54	11.187%	$200.737	$200.74	$200.75	$200.70
Purchase #4	$159.46	9.709%	$174.942	$174.94	$174.95	$174.90
Purchase #5	$109.80	12.144%	$123.1341	$123.13	$123.15	$123.10
Purchase #6	$80.51	12.196%	$90.329	$90.33	$90.35	$90.30
Purchase #7	$76.38	3.813%	$79.2924	$79.29	$79.30	$79.30
7 purchase totals =	$905.81		$980.2794	$980.27	$980.30	$980.20