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	$75.51	9.262%	$82.5037	$82.50	$82.50	$82.50
Purchase #2	$170.77	11.311%	$190.0858	$190.09	$190.10	$190.10
Purchase #3	$136.37	11.583%	$152.1657	$152.17	$152.15	$152.20
Purchase #4	$99.71	10.542%	$110.2214	$110.22	$110.20	$110.20
Purchase #5	$86.37	5.451%	$91.078	$91.08	$91.10	$91.10
Purchase #6	$48.57	6.118%	$51.5415	$51.54	$51.55	$51.50
Purchase #7	$135.77	9.658%	$148.8827	$148.88	$148.90	$148.90
7 purchase totals =	$753.07		$826.4788	$826.48	$826.50	$826.50