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	$55.27	5.314%	$58.207	$58.21	$58.20	$58.20
Purchase #2	$85.58	4.469%	$89.4046	$89.40	$89.40	$89.40
Purchase #3	$103.47	8.451%	$112.2142	$112.21	$112.20	$112.20
Purchase #4	$50.67	4.314%	$52.8559	$52.86	$52.85	$52.90
Purchase #5	$96.68	9.492%	$105.8569	$105.86	$105.85	$105.90
Purchase #6	$19.69	11.583%	$21.9707	$21.97	$21.95	$22.00
Purchase #7	$67.46	3.585%	$69.8784	$69.88	$69.90	$69.90
7 purchase totals =	$478.82		$510.3877	$510.39	$510.35	$510.50