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	$142.38	3.794%	$147.7819	$147.78	$147.80	$147.80
Purchase #2	$231.36	6.281%	$245.8917	$245.89	$245.90	$245.90
Purchase #3	$215.67	13.233%	$244.2096	$244.21	$244.20	$244.20
Purchase #4	$151.94	7.237%	$162.9359	$162.94	$162.95	$162.90
Purchase #5	$198.76	4.724%	$208.1494	$208.15	$208.15	$208.10
Purchase #6	$139.51	9.846%	$153.2462	$153.25	$153.25	$153.20
Purchase #7	$148.69	12.384%	$167.1038	$167.10	$167.10	$167.10
7 purchase totals =	$1,228.31		$1,329.3185	$1,329.32	$1,329.35	$1,329.20