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	$133.74	7.108%	$143.2462	$143.25	$143.25	$143.20
Purchase #2	$98.74	4.505%	$103.1882	$103.19	$103.20	$103.20
Purchase #3	$121.81	7.665%	$131.1467	$131.15	$131.15	$131.10
Purchase #4	$110.51	5.105%	$116.1515	$116.15	$116.15	$116.20
Purchase #5	$53.93	12.769%	$60.8163	$60.82	$60.80	$60.80
Purchase #6	$37.41	13.402%	$42.4237	$42.42	$42.40	$42.40
Purchase #7	$67.63	13.445%	$76.7229	$76.72	$76.70	$76.70
7 purchase totals =	$623.77		$673.6955	$673.70	$673.65	$673.60