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	$64.78	11.392%	$72.1597	$72.16	$72.15	$72.20
Purchase #2	$231.51	7.808%	$249.5863	$249.59	$249.60	$249.60
Purchase #3	$141.69	13.157%	$160.3322	$160.33	$160.35	$160.30
Purchase #4	$117.32	9.234%	$128.1533	$128.15	$128.15	$128.20
Purchase #5	$77.47	4.501%	$80.9569	$80.96	$80.95	$81.00
Purchase #6	$30.93	7.221%	$33.1635	$33.16	$33.15	$33.20
Purchase #7	$196.68	11.473%	$219.2451	$219.25	$219.25	$219.20
7 purchase totals =	$860.38		$943.5970	$943.60	$943.60	$943.70