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	$74.81	11.587%	$83.4782	$83.48	$83.50	$83.50
Purchase #2	$129.31	9.328%	$141.372	$141.37	$141.35	$141.40
Purchase #3	$114.25	9.758%	$125.3985	$125.40	$125.40	$125.40
Purchase #4	$233.71	6.121%	$248.0154	$248.02	$248.00	$248.00
Purchase #5	$149.64	7.521%	$160.8944	$160.89	$160.90	$160.90
Purchase #6	$17.71	4.750%	$18.5512	$18.55	$18.55	$18.60
Purchase #7	$83.80	8.220%	$90.6884	$90.69	$90.70	$90.70
7 purchase totals =	$803.23		$868.3981	$868.40	$868.40	$868.50