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	$167.91	3.366%	$173.5619	$173.56	$173.55	$173.60
Purchase #2	$102.25	8.371%	$110.8093	$110.81	$110.80	$110.80
Purchase #3	$28.55	9.469%	$31.2534	$31.25	$31.25	$31.30
Purchase #4	$54.96	8.758%	$59.7734	$59.77	$59.75	$59.80
Purchase #5	$225.87	7.656%	$243.1626	$243.16	$243.15	$243.20
Purchase #6	$48.91	10.849%	$54.2162	$54.22	$54.20	$54.20
Purchase #7	$179.77	3.240%	$185.5945	$185.59	$185.60	$185.60
7 purchase totals =	$808.22		$858.3713	$858.36	$858.30	$858.50