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	$160.76	4.224%	$167.5505	$167.55	$167.55	$167.60
Purchase #2	$163.96	4.160%	$170.7807	$170.78	$170.80	$170.80
Purchase #3	$129.56	8.522%	$140.6011	$140.60	$140.60	$140.60
Purchase #4	$100.79	10.666%	$111.5403	$111.54	$111.55	$111.50
Purchase #5	$227.40	8.127%	$245.8808	$245.88	$245.90	$245.90
Purchase #6	$210.91	13.438%	$239.2521	$239.25	$239.25	$239.30
Purchase #7	$185.53	5.721%	$196.1442	$196.14	$196.15	$196.10
7 purchase totals =	$1,178.91		$1,271.7497	$1,271.74	$1,271.80	$1,271.80