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	$64.41	4.631%	$67.3928	$67.39	$67.40	$67.40
Purchase #2	$214.80	7.696%	$231.331	$231.33	$231.35	$231.30
Purchase #3	$16.77	9.365%	$18.3405	$18.34	$18.35	$18.30
Purchase #4	$67.70	5.437%	$71.3808	$71.38	$71.40	$71.40
Purchase #5	$82.36	12.237%	$92.4384	$92.44	$92.45	$92.40
Purchase #6	$44.25	13.766%	$50.3415	$50.34	$50.35	$50.30
Purchase #7	$29.28	6.724%	$31.2488	$31.25	$31.25	$31.20
7 purchase totals =	$519.57		$562.4738	$562.47	$562.55	$562.30