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	$57.67	5.816%	$61.0241	$61.02	$61.00	$61.00
Purchase #2	$103.60	7.627%	$111.5016	$111.50	$111.50	$111.50
Purchase #3	$123.66	6.807%	$132.0775	$132.08	$132.10	$132.10
Purchase #4	$125.95	9.227%	$137.5714	$137.57	$137.55	$137.60
Purchase #5	$50.91	3.861%	$52.8756	$52.88	$52.90	$52.90
Purchase #6	$71.84	4.213%	$74.8666	$74.87	$74.85	$74.90
Purchase #7	$71.35	11.215%	$79.3519	$79.35	$79.35	$79.40
7 purchase totals =	$604.98		$649.2687	$649.27	$649.25	$649.40